Shawn,(posted 8746 days ago)MF is the right tool for the job. I personally do not think that the P67 is the right MF system [I've had direct experience] because of its limitations for syncro sun work, etc.
35mm will yield different results than MF, just as LF is different than either of those. Format dictates technique. The point is, each has strong/weak points. To shoot fashion [live, moving people] with studio lighting [non TTL flash] in difficult mixed lighting conditions, add being "tricky" [your personal style] with any kind of dynamic energy captured in the final image, and the answer is MF.
Now, your choice of systems was probably the result of the P67's low $$$ allure, but now you are growing past it's abilities, and finding its limitations, you need more capability for this kind of work. I'm with the "get a different MF" group. Bite the bullet and do it right. If you bail on MF and go back to 35mm, I'll guarantee that the first time [and every time there after] you nail a shot and look at it on the light box, you'll have a nagging little voice in your head that is saying "I wish this was on 120"......
At a minimum get a second P67 body with a Polaroid back, at least then you can see what the hell you are doing. It is worth the investment in time and energy to become a proficient MF shooter, there are very few people who have the dedication to do so, because its too hard [insert whining voice here].
Gooooooooood day!