I was thinking about this some more and wanted to offer a bit more info. At almost every race event we have here in the Midwest we end up having classes that get red flagged (stopped) due to crashes, the irony is that the same classes are usually the culprit with the number one group being the middleweight classes. The middleweight classes generally have the largest number of entries so the amount of people surrounding you on the track at any given moment is greater, this basically means you have less room for errors by yourself or by those around you. I personally try and shy away from suggesting the Middlweight class for new racers due to the chaos that so often ensues, but if you wanted to get a true 'trial by fire' that would definately be the class for it.
Another factor is 'Power to Weight Ratio' (P/W/R), I mention this quite often because it's a very real factor in racing that so many people are more or less oblivious to or don't realize just how much of an impact it truely has. P/W/R has somewhat of a 'bell curve' effect in racing, at certain stages of learning to race excessive power will give somewhat of a false sense of accomplishment as a person starts to grasp some of the principles of going fast on the track. A very common situation is a newer racer on a bike with some Horsepower (Hp) going really fast down the straights, then 'late braking' because they've heard other racers talking about how they got past someone doing that, then because they generally over-braked they completely blow their corner speed (commonly refered to as 'Parking it in the turns' - very common of inexperienced racers, especially on higher Hp bikes). The big advantage to having a lower P/W/R on the track is not having to worry about traction near as much and concentrating on corner speed to improve your lap times - not Hp. This is where that 'bell curve' comes into play, with a higher Hp bike you may see your lap times drop rather quickly in the beginning, then hit somewhat of a plateau when you find you can't really go too much faster on the straights or brake any deeper into the turns (though you'll go faster as you get more experience over time and learn to carry more speed thru the turns). With a lower Hp bike you may find you don't percieve as big of an improvement in lap times as soon you would on a higher Hp bike, but what you are learning is something very valuable - corner speed. I know what it was like when I started racing back in '96, I wanted to go fast! But looking back now I know I wasted alot of time by starting out on my GSXR750 and constantly having to worry about loss of traction in the turns from excessive power.
The way to calculate P/W/R is thru simple math, all you need to know is the combined weight of you on your bike as it will be raced (fuel and race gear included) and the rear wheel Hp of your bike. There's 2 main ways to calculate P/W/R, one creates a ratio showing Hp per pound, the other shows pounds per Hp. For Hp per pound divide the rear wheel Hp by the combined rider/bike weight, for pounds per Hp divide the combined rider/bike weight by the rear wheel Hp. Using 400 pounds for the bike weight, 150 pounds for rider weight, and 125 rear wheel Horsepower the ratio's would be as follows:
125 Hp divided by 550 lbs = .22727 Hp per pound
550 lbs divided by 125 Hp = 4.4 lbs per Hp
As an example at my last race event there was a racer who passed me in every race, on the straights they would just run away from me, in that case their P/W/R advantage was huge! This person was riding a late model GSXR750 (should be apx 142 Hp and about 400 lbs wet weight) and I'm guess they only weighed about 110 pounds (with gear), for comparison I will show what would be required for me to have the same P/W/R as they do. My '02 GSXR 750 (apx 400 lbs wet weight) had 132 rear wheel Hp when I had it dyno-tuned back in 2002 (even though I would imagine after 6 years the Hp is now lower I will still use that original Hp number) and I weigh about 240 lbs with all my gear on.
My P/W/R:
132 Hp divided by 640 lbs = .20625 Hp per pound
630 lbs divided by 132 Hp = 4.84848 lbs per Hp
Their P/W/R:
142 Hp divided by 510 lbs = .27843 Hp per pound
510 lbs divided by 142 Hp = 3.59155 lbs per Hp
These numbers alone don't mean too much until you use them in a real world comparison. For me to have the same P/W/R as the other racer I would take my combined rider/bike weight (640 lbs) and multiply it by their Hp per pound ratio (.27843) :
640 x .27843 = 178.1952
So for me to have the same P/W/R as the other racer I would have to have 178 rear wheel Hp! Working the comparison the other way we can figure what Hp they would have to have to be equal to my P/W/R, to do this we would take their combined rider/bike weight (510 lbs) and multiply it by my Hp per pound ratio (.20625) :
510 x .20625 = 105.1875
This means that the other rider would only have to be on a basically stock late model 600 with apx 105 Hp and we would be equal in P/W/R. The fact that they not only weigh 130 lbs less than me, but also have 10 more Hp, is a massive disadvantage for me.
The reason I went thru this P/W/R explanation is to make the point that if you don't want to just concentrate on developing your corner speed and want to go with a bike that has more power than an SV650 you should consider P/W/R in your choice. Because your heavy like myself your going to be at a significant disadvantage to the other racers in the Middleweight class if you choose to go with a 600. The advantage for you on a 600 will be a lower P/W/R than the other racers in the Middleweight class, the reason that's an advantage is the chances of you spinning the rear wheel will be significantly lower (but unfortunately your weight will force your tires to work harder than a lighter racer carrying the same speed thru the same turn - somewhat of a double-edged sword of gaining somewhere then losing that advantage somewhere else). Some disadvantages will be that you will get out-powered on straights and have to brake sooner due to having to slow down more weight, what this will most likely result in is the other racers getting by you not only under acceleration, but also on the brakes.
Based on what I've seen there's a point where you go from having good power to excessive power, the point where you have the power to start spinning the rear wheel on acceleration and have to be alot more careful on throttle application (but certainly not saying it won't happen with a lower P/W/R, it's just the chances are alot lower). These are numbers I have come up with myself based on my personal experience, so your not going to see this somewhere else (at least I've never seen it listed in this way). That point where you start to have excessive power is around (.2) Hp per pound, that works out to apx (5) lbs per Hp. Since the 600's thru 1000's are all apx 400 lbs wet weight that would make your combined rider/bike weight (with 10 lbs of gear) apx 630 lbs on those bikes, multiplying that 630 lbs times the (.2) Hp per pound I just mentioned your excessive Hp power point would be apx 126 Hp. The more you increase your Hp per pound ratio (more than the .2 ratio I mentioned) or decrease your lbs per Hp (less than the 5 lbs per Hp) the more difficult the bike will be to apply that power to the ground. Remember these are ballpark figures and not exact numbers, other factors like tires / track conditions / body positioning / racing line thru a turn / excessive speed and more can all cause loss of traction.
I hope this sheds a little more light on helping to make a decision on which bike to buy.
What bike to start on in CCS?
) so while I may be an experienced racer, there was still some theoretical applications I obviously missed. 
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