Hi, I took my bike into the shop today to get repaired, and two bikes caught my eye, the Trek 4100 Alpha and the Trek 820. I am planning to buy one of these bikes when I go back to get my Trek 6500(it's getting repaired). I went on the Trek site, and it shows that the 820 has a steel/cro-moly frame while the 4100 has an Alpha Aluminum frame.. I realize that the 820 is going to be heavier and stronger, while the 4100 is going to be lighter and weaker. Is the 4100 going to be that much easier to ride because of the weight difference over the 820? The 4100 has a InSync Grind 320 fork (70mm travel) while the 820 has a RST 191CL fork (63mm travel) I am mainly going to use this bike to commute around. I already have a Trek 6500, so this will be my second mountain bike. Thanks!