A flatbed will pull out a sharp 30-40mp equivalency of 4x5" if that's the road you're looking at and are keen on detail level. The sensor output is also trash and cannot compare to a dSLR in other arenas of quality, the only advantage here is the larger size vs smaller size.

Don't want to see you invest and then get disappointed. I'd suggest finding someone who shoots 4x5" and scans, and getting to look at their images and see if it's suitable for you.