I had an 01 321, loved it, was half scared when I traded it of and got an 07 300. The 321 was a great bike, no real problems with it. The pro is lighter, has more power but still carries the low end torque that I loved on the 01. Big difference in the suspension and the brakes. The 300 wins easy after riding through water, brakes actually work which wasn't the case with the 321. Can't really tell you what the difference in the shocks/forks is but the pro stuff is way better. My advise, by the pro unless you are just going to trail ride, if that's the case the 321 might be better but for trials the 300 is a better choice. Only beefs with the 07... you have to learn to start it, all the pros are like that and I never have taken a liking to the shifter, just doesn't feel right, we have had 4 pro models at our house and they all are the same in both respects.