The number of G forces the human body can withstand relies entirely on the orientation that they are being applied. Imagine a person standing straight. If they move up, a trained foghter pilot can withstand up to 9 Gs. Moving down, you get about 3 Gs before your eyes explode. Moving forward, however, let's you survive up to 45 Gs, though not necessarily uninjured. Assuming this spell moves you forward, the acceleration is well within the range of survivability, and the only issue is getting flayed by air resistance. So, assuming that magical flight takes care of that part, the spell is actually perfectly fine, so long as you don't use it to rocket upwards.