The 75mm may or may not cover the larger negative, you won't know until you try. A 75mm lens would likely be designed to enlarge 645 or maybe 6x6 negatives. Going from 6x6 to 6x7 you're increasing the image circle by roughly 18%, so that's how much more you ask of your lens to cover.
I recommend testing it, with four 8x10 sheets like 'seadrive' above suggests. See if you have coverage and sharpness all the way out to the corners.
The whole print size thing is interesting. I print most of my work on 11x14 paper, but some on 16x20 and some on 8x10. Whatever the series of pictures dictate. I'm printing a series of forest scenes on 16x20 because they possess a certain grandure that I think would be lost in smaller size. Neg size from 35mm to 5x7. I'm also printing some 6x6 pinhole shots as 8x8" on 11x14 paper, because they seem to just look better that way, and communicate the ethereal quality of the pinhole more effectively. And on and on.