Yes, the GV is ex$pensive, also the OD ratio isn't as slow as the 518 (69%).
518 advantage: lock-up converter.
Also:
Shorter driveshaft means more pinion angle change.
Drive-shaft speed is not reduced by OD, so very high MPH is a bit dangerous.

Re: makes me want to black out
Easy + cheap cure: inflatable weight-loss pants (eBay), uses air pressure to compress the legs and thighs - this is where the blood goes on hard G, starving the head. Test pilot/astronaut suits do the same thing, but they aren't cheap!