You don't mention the most important things, like how many concurrent users, what types of pages, how fast of a network link, and that good stuff. Any server will be fast if not doing anything!
And what is SPS?
Things that would have made it faster are:
-having another hdd, then you could have two mirrors (on separate controllers), one for OS, one for Apps
-Hopefully you're using HW raid, not sw
-For the $$ you saved on the 2650 v the 6450, you probably could have bought two 2650's one for IIS, and one for SPS