My buddy hit 100mph with your exact gearing/setup except hes running the same lipos as me.
I hit 93mph tonight on the car's first run, VERY impressed thus far. As far as the pinions go the largest that will fit with my conversion I'm using a 25tooth on the 1st gear of the rc-monster 2speed conversion, I will try to fit a 29tooth on the 2nd speed but i need the "long shank motor plate" from tekno first. I will break 100 within the coming days and I will get video of both me and my buddies ASAP. Had an unfortunate blow over at near top speed and i was not running a wing at the time, resulting in the most painful lid skid I'd ever had to endure. The result? nothing more than a scratched front shock tower and shaven down wing mount.
Here's some pics of my finished buggy:

Oops...