Neutral grip (parallel grip) has less carry over to barbell benching, but allows greater ROM and is a little friendlier on the shoulders.
In terms of your 85lb DB's, have you tried cheating them up? if you can ten rep the 75's with good controlled technique the 85's should be a piece of cake. Cheat up the first rep and the rest should be easy. If you definitely cannot manage, keep working with the 75lb ones, doing more difficult movements like one arm benching, extra wide grip and deeper range (like a pseudo fly or even full fly if you can manage), inclines, standing DB push press, tricep extensions/skullcrushers etc. The 85's will soon become easy, you can also microload the 75's by sticking anything moderately heavy to them.