This may be a little late but...............
I scan 6X9 and occasionally 4X5 film on an Epson v750 Pro, "pro" meaning that Silverfast and other software was included with the scanner. A 6X9 at 2400 dpi gives me a 400Mb 16bit tiff file. The size of a multi-layer image after P/S can be stagering.
The primary reason that I tried the scanner route was that I wanted to use my existing set of Schneider lenses on a 4X5 Toyo with a roll film back. These lenses are very sharp corner to corner with very little CA. I don't have nor can afford the latest top quality DLSR lenses and or a MFDB system. I also enjoy a complete set of movements, something that is often over looked in these discussions. The biggest short fall is in DR.
One common complaint with flatbed scanners is that the film holders are difficult / impossible to get sharp focus, even if you purchase a robust aftermarket holder. I didn't bother, I went directly to fluid mounting, with good success. It is time consuming. I don't do every frame so this isn't too much of an issue for me. I do this only for selected images that will be printed large. I have done side-by-side comparisons against my DLSR using excellent techniques, (cable release, manual focus, MLU, time delay etc) and against a few 4X5 B&W negs / prints. The scanned results are acceptable to surprisingly good. After enlarging to 24"+ the prints are better than my 24meg DLSR but certainly not as good as a 60-80 meg MFDB. I would guesstimate that the cross-over in quality is approximately comparable to a 40 meg back. Below the 24" size, I'm not sure that it's worth the cost and effort.
A drum scan will cost you anywhere from $50 -$200 each. So you can calculate the ROI for a flat bed scanner, it can be a very short payback. I justified the experiment after realizing that I could always sell the scanner on e-bay. All in I think that I have less than Cdn$1000 invested.
This works for me.