Properly mounted roof racks, with no limitations (weight limits etc), should be good for insane speeds. I won't vouch for the vehicle. RV-Inno (or Inno), a Japanese rectangular bar company, tests their racks on Honda's high speed track. They typically go a minimum of 200 kph/124 mph in their tests. They also have the bumpy off road course, I think they go like 30 kph over about 1 foot bumps and you should see how much a hitch rack flexes (!).

I've driven unofficially at 100-110 mph for sustained periods of time (~40 hours in 10 days) with 4 bikes and 4 extra sets of wheels on a roof rack with no problems. Well, we killed the (1.6l) engine, but otherwise... I've also hit 120 mph with a short roof line rack with 2 bikes, sustained 80-95 for ~100 hours in 4 weeks (various wind - from nothing to really windy). Ditto on the (2.3l turbo) engine (did a 10k mile trip, then went 50 more miles and died).

Roof racks really kill your mileage. Hitch racks not so much.

However, with a hatch, I say roof. Like DrPete said, hatch + rear mount = PITA.

cdr