Tdub has hauled my but up to 84mph on a couple of occasions--downhill, tailwind, drafting a semi. Maintaining 70mph in city freeway traffic is pretty easy because all the other vehicles seem to keep the air flowing in the right direction. Much easier than maintaining 70mph on a rural interstate. I took Tdub out on a limited access highway yesterday, about level with light SW wind, 70mph west-to-east, 72mph east-to-west, tucked in, 8-10mph less sitting up. Had I been running E10, Tdudb would have been doing good to hit 60mph sitting up. On the westbound leg a SUV eased past running 76, then Tdub sped up to that pace just by moving over to the dotted line without changing lanes to take advantage of the draft. When I hit the highways I pretty much tuck in on the uphills and sit up on the downhills, and the speed doesn't much vary.
Minor tooth-count changes won't make a lot of difference in top speed unless riding off a cliff--TW powerbands are just too flat. Better rollout in low gears and less vibration are street benefits of a slightly taller sprocket ratios, no greater than the equivalent of a 14/45 set. More than that and clutch wear and excessive rpm drop between gears become issues. Better low-speed response and compression braking are offroad benefits of slightly lower sprocket ratios, no less than the equivalent of a 14/55 set. More than that and 1st gear becomes useless on the street and vibration at speed becomes annoying.