I have had the 35, 40, and 24F0 cans on my DR, with the air box/jetting mods... I would be happy with any of them; the difference, in a nutshell:
40f0; 4.5#, sounds better, flows a LOT of air
35fo; approx 7#, same size as the 40, still sounds great
24F0; same weight as the 35, slightly longer, my DR seems to like this one the best, has the perfect amount of restriction.
I have a pumper carb and oversized header on the way from Kientech.com; interested in how the different header will affect my torque, should know by the end of the week.