The posting of threads is messed up. This was not the original post to this thread, it should be about #8 in line and I have no idea who started the thread.
I have been re-reading a lot of technical books and have come to thee conclusions as Barry Thornton. Deciding on a format depends on the size of enlargements you are going to make. With the best gear, using medium speed film and a high acutuance developer (perceptol, Pyrocat, Dixiactol) the best you can get from 35mm is about 8x10 before you start to lose sharpness and see noticeable grain. Of course that is if you are looking for a high degree of apparent sharpness.
MF, 6x6 and larger alows you to go up to 16" prints and on up.
Thornton was only interested in making the sharpest appearing prints possible, so if that is not as important in your work then it would not be applicable.
Also, from what I understand re-reading Edge of Darkness by Thornton unless you specifically require movements or enlarge over 16x20, you get no advantage from using 4x5 over MF.
This would also not be applicable to a contact print, as an 8x10 contact whould be sharper then an enlargement from the best MF if good techniuqe and lens was used with the LF.