If you're aiming for 1500+, I doubt a study buddy will help much since most of the studying is just memorizing vocab.

The reason that an 800 math only gets you a 94% is because 1. you are competing against a much smaller and smarter group of test takers as compared to the SATs (everybody takes SATs, not everybody applies to grad school), 2. you are competing with a lot of international students who are very strong in math.