My points on this was ment for Wil not in general as i still love cossies , but if you price up building and running a sorted spec 500 bhp escos then you are easily into 996 money.
When i did the last changes to mine i tried to spec everything to keep it reliable and it still gave hassles.
I also agree that there will be loads of cosworths on the road quicker than 996's but your talking heavily modded cars against a standard car, do a few mods to the porker then see what happens.