And most will say what are goals with car? Staying N/A? 70mm might be better gains than a 75. Although a 75mm will still be more than stock. It won't hurt you by any means.
If getting n2o or FI get a 75mm for sure. If getting all bolt ons with heads and cams.. i would probably get a 75mm, but it could be argued both ways i think.
Major thing is whats your end game for the car? I ended up selling my 70mm for a 75mm because i didn't plan ahead.