Back to the OP;
I starting a new fine art portrait project which could entail printing super large down the road.
For those in the know, who have really used all the various size cameras, for printing real large, what have you discovered -- i.e. medium format -- Mamiya Rz for example (film vs Digital)/ vs the best dslr (Canon 5D2 for example which I have and know)
I have never used 4x5 or 8x10 personally, but for those conversant -- how does the Canon 5d2 // medium format digital//, stack up? This is for the few who have actually done A:B tests.
More or newer gear will not necessarily get you better pictures, since it takes time to learn the new tools.
The best camera is often the one we have, if it feels comfortable as a tool in our hands. A TOOL
is all a camera is, but it helps if it is one we enjoy working with and see images well through.
Thus I would advise to stick to your 5D2 and perfect your shoot from all ways possible with the images in mind. However, if you want to use also a second camera, why not pick up a used RZ on ebay with just one single lens, the standard 110mm. They sell for near free nowadays! Use film. If you like the results you can pay to make some drum scans. If proper exposed and proper light they will most likely blow your images from 5D2 from water based on image quality (do pay attention to DR of film and expose accordingly). If you get hooked, keep it and see what future where will lead
Be warned, the view from a waist level finder can make you hooked. Looking through such in RZ, Hassy 503, made me go for Hy6 and I am having a ball capturing images that way. It is a brilliant way of seeing and viewing a subject when shooting. Sort of half way towards staring at groundglass on a viewcamera. DSLR viewfinders are small and dim...