YEAH ANOTHER AUSSIE! :beer Damn i bet its cold down there now. It sure is here.
In my (limited) experience:
A 4 will rev harder, burn more fuel, and produce more kilowatts than a twin. The twin produces more torque/ pulling power, will have smoother power delivery, idles, runs better at low revs and cold.
My 250 was an inline4, it was smooth as down low and had a good powerband when going nuts. My bike now is also inline 4. I reckon they are better JMO. When test riding, before upgrading, i rode an 850 twin, newer than mine. It sounded KICK ASS but the inline 4's (600's) were just as smooth down low and a rocketship up top. Some people say that inline 4's are too peaky. While i accept this, my bike rides VERY WELL and smoothly at around 6 grand, cruises effortlessly. Then when i give it a rip through a corner, or overtake, i get a grin factor i couldnt get on the (b*****) twin, the response of the 4 is amazing.....
Gotta love that sound though

hatyo