I have tried the typical studio portraiture with a 3-light setup, backgrounds and Nikon DSLR's...but they are a dime a dozen and do not have any character, at least IMHO.
this has nothing to do with the equipment and everything to do with the operator of said equipment. The only reason for "dime a dozen" is the lack of creativity from the photographer. There are people out there that have done one light setups that just blow my mind.
I use an M in the studio exclusively and every day is a new challenge. Studio portraiture is going to be all about your lighting however, and very little about whatever camera you use. I stick with the M as its the shortest route to me realizing my ideas.