I spent much of today helping a friend who is new to medium format and close to new to darkroom work. We were working on an 11 x 14 print from one of her first rolls shot with a Bronica ETRs. In this case, she used a tripod.
The detail we were able to reveal in her print was wonderful. The shot, which I believe was on FP4+, could easily have been enlarged to 16x20.
I regularly get similar results with my Mamiya 645 Pro and either Plus-X or TMY-2. And I regularly get transparencies that are both a joy to project and, when scanned, give excellent 12x16 colour prints.
If you print rectangular photographs, 6x4.5 is capable of the same quality as 6x6.
I also shoot 6x6 and 6x7. The negatives from those cameras are also good to print.
Finally, I shoot 35mm film as well. When I print to something like 11x14, I can usually get results I am happy with, but I definitely prefer 6x4.5 negatives, because they are substantially larger than their 35mm cousins.
Either an ETRS or a 645 Pro is a fair bit more bulky then my 35mm eqipment, but it is similar in size to some of the digital equipment out there.