My car has some vibrations here and there but at higher revs it's quite smooth. It will easily attain 50+ mph on the flats, but can't say that I feel comfortable at that speed... 45 seems happier.
There is talk of a drive being put together by some local clubs beginning in Blaine, WA and traveling to Mt. Baker. It's a bout a 70 mile trip but the last 20 miles climbs 4000+ feet in elevation, and the last 8 miles has a lot of switchbacks as it climbs even more steeply. Sounds like maybe some sustained 25mph in second gear is doable?