Tell me how it compairs to your CAAD5? I currently ride a CAAD10.
That's a tough one, especially since I believe the CAAD5 isn't really easy to compare to a CAAD10 as well... As far as I remember the CAAD5 was probably the stiffest and harshest road bike Cannondale ever made. So brutal, that even the Pros couldn't cope with it. This is why they replaced the CAAD5 in the middle of the Season with the CAAD6.
That said: I love my CAAD5. It's an extremely light bike (built it up with Dura Ace 7700, and Easton EA90 Aero wheels it's astonishing how light it is). There's no carbon fibre touching that bike... It's playful and fun to ride... but that mean's fun as in "Skateboarding" or being in a jump arena... Really fun, really crazy... but after an hour of riding it you suddenly realize you're not 16 anymore. Some of my best timed laps were made on that CAAD5 and (even at comparable fitness level) I couldn't compete with any of the carbon bikes I've owned later (Cannondale Slice as a Road build, BMC Teammachine SLR02) - as long as the laps ware under an hour. The moment I'm looking at the two-hour laps the CAAD5 is like 15 minutes slower than the others.
So with that in mind: the main difference is comfort vs harshness. The GT feels plenty stiff and every pedal stroke seems to propel you forward really well. I'd say in that regards it's probably the closest to how the CAAD5 felt to me (meaning: BMC, Cannondale Slice, CAAD9, my CX bikes, Focus Cayo, my steel steed, Klein Quantum Race, Principia felt more sluggish than the GT and the CAAD5). Riding on flats, seated, without moving the bike around too much I'd say the GT feels similar in accelleration to the CAAD5. In all out sprints, I believe the CAAD5 feels quicker to me... this might be due to nostalgia or due to the fact that the GT (with 34 Vittoria Corsas) eats up small bumps and road chatter... So I'm not sure which of the two would be more effective in an all out sprint...
Comparing the CAAD5 to the GT seems like: Go-Cart without suspension compared to a magic carpet flying 10 cm above the ground...
The racing cart feels fast - my family car goes faster on the motorway... the magic carpet probably is another level...
Hope that helps
Cheers
Robert