The CAAD 8 2300 and CAAD 8 Sora will both have a compact double crankset--two chain rings, one 34 tooth and the larger 50 tooth. The difference will be the rear cogset, or cassette. 2300 is Shimano's lowest level system, with an 8 tooth cassette and a 2300 rear derailleur. The Sora is one step up, with 9 teeth on the rear cassette. If you're looking at 2013 models, the Sora shifters now operate like the higher end Shimano shifters. To shift to a lower gear, you move the brake lever towards the inside. To shift to a higher gear, you use the secondary lever behind the brake lever. The 2300 shifters still use the older system, where you downshift off the brake lever, but use a thumb button on the top of the shifter to shift up. The problem is that you can't reach the button if you're holding the bars on the drops, which makes it a poor choice for racing
The CAAD 8 triple has three chain rings up front, 52/42/30 teeth, respectively. You must be looking at a previous-year model, as Cannondale doesn't list a triple for 2013 models.
If I were you, thinking of racing sprints and tris, I'd be looking at the next step up, Tiagra, at minimum. Tiagra has a 10 cog cassette on the rear.
