I think after about 40 inches getting solid prints from 35mm is a crap shoot, and depends a lot on how perfect the shot was and the subject matter, I also think a lot of the problems from big 35mm prints comes from lens choice. But again I think sometimes you can get really nice big prints from 35mm
I don't shoot 35mm anymore, I do tons of printing but all to developed film using lightjet, this in itself probably makes big 35mm prints seem nicer, but everything I shoot now has the potential to be done as a big print, so I don't risk shooting 35mm.
I also feel the quality of the gear in MF to be much better than 35mm and a lot of the lenses superior in every way.
I think in the print size of 36 to 72 inches MF will just shine against 35mm in a more consistent manor, in that more of your shoots will look great big.
After 72 inches I don't know how even MF will hold up when examined critically, as you are starting to up sample a lot by then, and things start to smooth out, a couple of my friends start to add noise on really big prints to counter balance this.
I guess there are so many variables depending on camera, subject, post work, etc...