Quote Originally Posted by Thomas Bertilsson View Post
Personally I don't see a need to get a bigger negative (and camera) if you print 16x20 or maybe even 20x24. If you stand more than three feet away from the print, you're not likely to spot much difference. It depends a little on what film you use.
A properly exposed and processed negative in 645 format will yield a virtually grain free 16x20s. Heck, shooting Acros/Xtol in 35mm I get almost grain free 16x20s; you'd have to press your eye up against the print surface to see it.

My advice - In interest of the pictures themselves, you're best off shooting the camera that feels the most natural in your hands and fits into your work flow best. Unless you like to look at your prints with a loupe. Those are my two cents.
What he said. I develop 35mm Acros in Pyrocat and Xtol and so far 11x14 are sharp and without any grain...quite remarkable really. That being said, a MF neg has more fine details, which can have a dramatic effect on the overall image/composition.