How big do you want to print? Honestly, if it's 16x20 or smaller, you won't want for quality from a 6x7 negative. I've printed tripod mounted RZ portraits that large that show threads in the fabric. Yes, a 4x5 neg will be sharper, it will also cost more, and you'll shoot less, and slower. That may be a good thing, or it may not. If you're the kind of photographer who likes to conceptualize everything before releasing the shutter, 4x5 is great. If you prefer spontaneity and shooting from the hip, go with the 6x7. I shoot both 6x6 and 6x7 and love them both long time. My 4x5 doesn't get much love.