Joseph, your last comment is what interests me. DSLR imaging at 0.5X allows a four fold increase in the field of view. A 24 X 36 mm field at 1:1 becomes a 48 X 72 mm. field at 0.5X. The detail referred to the sensor of course is reduced by 0.5X but a higher full frame pixel count can offset this - although a factor of 2 is a lot to compensate for. But full frame at 0.5X will nearly cover a 4X5 with four frames. The catch is probably in the quality of the lens. To make use of the intrinsic resolution of a 7 um pixel pitch sensor at 0.5X one needs a lens capability of close to 100 lp/mm at some reasonable contrast.
The only item I have to get started with is a 90mm, f/2.8, Vivitar Series 1 macro with 1:1 adaptor; although still highly regarded for its unusual resolution capability approaching the 100 lp/mm level. It is of notably low contrast however. I should try to find some resolution data on it. These are still available in the $400 to $500 range I believe.
On the other hand 36 MP X 4 will yield a 140 MP count on a 4X5, and GB+ files. I think most 4X5 images don't contain anywhere near that kind of detail. BTW that would be about 4 times the resolution I would normally get from my Epson 750 where I see a spot size equivalent of between 20 and 25 um. at reasonably high contrast. The full frame 20+ MP Canons seem ideal for this application as well as a new Nikon D800 - although very pricey - for me anyway.
But this would be my direction if financially feasible.
Nate Potter, Austin TX.