I run crazy low gearing on my 450. 50MPH is maxed out in 6th. I considered going lower than 17/42 on my 950 but just can't see wanting it geared any lower on the street.
Once I was on some wicked technical stuff and the 950 got hot from slipping the clutch to go slow. On the other hand, I use 6th on the pavement every ride to milk more range out of the fuel hungry beast.
2011 690 Enduro R
2013 Beta Evo
07 450 EXC