Engine tuning and the way you set up your tractor is all relevant. No power steering and hard-ass leaf springs on the highway can be very uncomfortable for many.
Whiteknuckling it all depends on the drivers insanity level. I had my Series One 2.0 up to 70mph without an overdrive this weekend. cursing speed 60-65 and its so insane and loud but I put up with it... and so did Josh.
I can't wait to instal my overdrive this weekend