Sounds like you need to go shoot film and avoid all these issues :-) If you're shooting MF and taking a long time over getting your shot right with regards lighting / exposure and composition, it would be silly for you to spoil your effort by shooting digital if very large prints are what you desire....
unfortunately I don't have the luxury of shooting film when I am dealing with a group of 20 people and only 5 minutes to get the shot. I have to get it and then finish the shoot in such circumstances, and digital's the only way. Abit of background on what I do so that perhaps you won't think I'm a raving lunatic.
I shoot large groups of people in outdoor environments using strobes. I started out shooting with my 1dsMkII, and then with a Rz67 and a Mamiya 7 once in awhile.
I started shooting 100G on 4x5 film for awhile but that didn't work out due to the lack of speed.
I scan my film on Imacon virtual drum scanners (funny...I prefer the Imacon to drum scans which seem to come out oversharpened and lacking grain usually for some reason)
I print my images up to 5ft for exhibition purposes so we're talking about putting your nose right in front of the print.
I exhibited two images, one shot with a 1DsMkII and one with a H39. now I know it's unfair to compare them since the resolution difference is astounding but one thing I noticed and have been noticing when uprezzing 1DsMkII files is that the interpolation causes edges to have a clumpy (for a lack of better word) look to them, after I sharpen the images.
The H39 file, which never seemed to look that great to me on the computer screen, suddenly popped out in print. everyone noticed it. The details were much finer, edge details especially.
The 1DsMkII file , which I absolutely adore and looks bloody good in my 13x19 portfolio, has a certain flatness to it. When I read on the Hot Rod page about how it looks like your image looks like there's a haze to it and it looks like a photo of a photo rather than a photo alone (does that make sense?), something went off in my head "Bingo!Exactly!"
The 1DsMkII files can look really great with careful processing, but frankly I've always felt that the files lacked a certain depth to them when printed. Editorially I could always tell that my file was a 1DsMkII file whereas it's pretty easy for me to point out when my peers have a film image.
This is just my personal opinion from all the work I've been doing.
Perhaps how the brain and eye perceives and digests visual information and ideas of depth and realism are more minute and diverse than just a simple theoretical explanation.