Well, I bit the bullet and got the Giant. I only have about 10 miles of riding on it so far, mostly shakedown type riding, but got in a few sprints and short hills so I can compare to the trail bike.
Wow this thing is fast!! I really didn't understand what they meant by an XC race bike until I rode this. Now I get it. It accelerates so quickly, uphills I'm in 5th gear versus 1st or 2nd on the trail bike. It is 9 pounds lighter which isn't trivial, but carbon wheels, fast tires, and geometry definitely come into play.
Handling is crazy, it turns so fast. Not nearly as stable as the trail bike, I would say it is almost twitchy/nervous, very racy. Really fun to throw it side to side.
For sure need to try my hands (legs?) at a race now!
