7.5 is gonna look kinda skinny for a 20" wheel especially when its spaced out more. But its hard to tell how many threads you have left. I thought I had plenty of space for a 10mm but when I actually got them on i couldn't even get the nut past 1 or 2 turns. And longer studs were a pain to change out, I had to take the whole rear hub assembly off and for my car it was rusted on pretty good