I'm in the same boat. Slightly torn between a 006 (with probably Contax adapter) and a 645z. I know the pros/cons for both.
As of late, I am leaning heavily towards the Pentax. I actually really prefer the 4:3 ratio. Also from my limited in-store test portraits with my wife....the Z had much nicer/neutral skin tones right out of the camera. The Leica had a sickly yellow/green thing going on. Plus the Pentax is just a much more versatile camera aside from the limited leaf shutter lenses....long exposures, low light, long lenses, live view....etc etc.
The Leica is just so sexy, it makes it a bit difficult. That viewfinder is to die for, and I like the interface. I would even consider it and getting a nice set of strobes and going full Studio/on location lighting guy....but tethering sucks for it. It also sucks for the Pentax, but at least there are some "work-arounds" for it.