Would anyone mind telling me the difference between the Trek 4300/4500's Aluminum SL frame and the Trek 6000/6700's Aluminum SLR frame? They seem about the same to me.
I live in Maine and I hate lobster.
Your observations are pretty much right . . . when it comes down to it, they are very similar.
They are supposedly lighter and stiffer. On the weight side of things a few years ago, i read that the difference was about 50grams . . .big wow.
Stiffness wise, thats possible i guess. The rear stays may have more forming and shaping to them which could increase the stiffness without any real weight differences.
On road bikes, the SLR frame seems to have smooth welding at the joins where as the SL frames have fish scale welds.
In terms of choosing a bike, i would put SL v SLR as a minor factor. The other things like wheels, gears and brakes are going to have a significantly bigger effect on how the bike performs and feels.