I am glad to here you are going with steel. They will definately last much much longer than aluminum.
As far as going down 1 on the front, and causing more wear. Yes this is true, but how much is argumenative.
My idea would be if you want quicker gearing you are far better off to keep the turning radius of the front as large as possible (its the tight turning radius that will create extra wear and also "steal" horsepower) so go with a larger rear sprocket and leave the front alone.
As far as availability of steel vs. aluminum. Yes alot of the aftermarkets want to sell you aluminum (they are cheaper and easier on equipment to produce and they can charge you more, by selling you on the lighter recipricating mass = more horsepower rhetoric.) There are websites out there that will sell you sunstar or parts unlimited or some other "off" brand steel sprockets front and rear. You just need to search..What is your time worth, to find the savings of $20 or so ??Whenever you can, get sprockets that are machined, not stamped!! Although some of the stamped sprockets are quite good, the machined sprockets are of higher quality 9 times out of 10.
( email me directly if you want, I own a service and repair facility and can get you into a complete set for a reasonable price. [email protected]
As far as chains go--The EK MZXV quadra x ring is the best (hands down no comparison) do you need the absolute best--probably not, plus it costs to have the very best.
The RK xso chains and the DID VM are excellent chains and will easily last 20,000+ with a little maintainance. ( I have a VM on my bike now with 25,000 miles on it, and I havent had to adjust it in over 10,000 miles--but I do lube it about every 300-500 miles depending on weather and riding conditions. ( while the did erv2 is lighter and boasts the same strength, its side plates are thinner and it stretches quite a bit, and again warranty issues of it being a "race chain"
Lastly sticking with the 525 chain disperses the load over a larger surface area, thus prolonging chain and sprocket life! Buut you will pay a little more for the 525 chain than that of a 520 chain--the sprockets cost the same.
Also if your bike came with a 525 and you change to a 520 kit, there usually will be no warranty, because that is considered a "race kit" regardless of your actual use.
Hope this helps. Lloyd