I have noticed the vignetting on my 500c/m when working with the cf120 makro-planar, especially when using extension tubes but it doesn't bother me much.
I would too go for the CF-series of lenses or newer (CFi/CFE) as these are smoother to focus, easier to set exposure and have better coating. Some people claim that there is a beginning shortage for parts to the older c/ct*-lenses, especially the flash contacts. The older lenses are almost as sharp as the newer, a few newer lenses have improved formulas which are said to give better results. I haven't had a chance to compare, but I did follow the advice to go for CF (I got a 60/3,5 and a 120/4, next one to come is the 250/5,6).
You won't be disappointed with a 'blad, they're fantastic! (But my opinion might be slightly colored, being from Gothenburg, Sweden =)