I've currently got a Pentacon 6, a Kiev 60, a Kiev 88CM, and a Mamiya 645AF. To counter almost everyone else, I've never had reliability issues with any of them, only once had overlapping frames (and I'm certain that I borked it when loading, and I can't even remember what camera it was)*.
I've got (almost) the full complement of lenses in P6 mount, Zeiss 50/80/120/180/300 and Soviet 30/65/80/90/250 (mostly multiple copies of each, I'll sell you some if you need).
The Zeisses are all fantastically sharp, but the soviet ones have their uses too (like my Volna has that petzval-esque swirly character in the right conditions), plus they're dirt cheap.
Best part is, they all also fit on my Mamiya 645AF via adapter, so I didn't need to buy into more lenses. But the P6 only goes as wide as 50mm (ok, there's the Mir45mm, but it's apparently not very good so I didn't get it).
So I've also got the Mamiya Manual-Focus 45mm and 35mm for the wide end. I'm not too impressed with the edge-sharpness of the 35mm (still yet to decide if it's typical or a de-centered element or something) but the 45mm is great.
Also consider that you can fit P67 lenses on M645 with an adapter (but not P67 on P6), the P67 45mm is very good from what I've seen, and costs not much more than the M645 45mm.
ps, I couldn't tell if you meant you wanted wider than 50mm MF, or 50mm in 135-equiv. If you want >50mm in MF, there's not much choice (only 1-2 lenses per system), but be aware of conversion-factors, ie a 45mm on 645 frames like a 55mm on 6x7 or 70mm on 6x9.
(*actually, for those concerned about P6-reliability, I've had more problems with my M645AF. On more than 2 occasions, halfway through a roll, it's "forgotten" that it had a film in and wound on as if it was starting a new one. So I've gotten a strip of blanks mid-roll, and I lose the ones at the end)