I've got a Diamondback Reactor Pro I'd like to use for some upcoming TT events. I've noticed that many pros race on small frames, so I figure I'll have an edge there too since smaller frames should be both stuffer and lighter. Plus, TT bikes often have smaller wheels, so I figure I'll have an advantage spinning up, particularly on hills.

I know I'll need skinnier tires and I've already picked up a set of Stelvios that should do nicely. But what parts of the bike do I need to upgrade? My budget is about $600. Thanks for any advice.