I have been exploring the options of using my 4X5 and a roll film back and the Epson V750-pro with a fluid mount rather than my Nikon D3 for some work.
Almost all that I have read and seen point to fluid mount scanning being essential to maximizing quality. This is something that few commentaries comparing DLSR vs scanning mention.
Another other point that I find to be persuasive in using the 4X5 is the cost of having to re-equip in top line DLSR lenses such as Zeiss or Schneider if even available for your choice in digital model. My 4X5 lenses cost in the neighbourhood of $2000 and are of course prime lenses. The very best DLSR lenses are certainly in this range. Dumping my investemnt on E-Bay won't cover starting over in the equipment race.
There are other points to consider too: the use of full camera movements, the flexibility of the DLSR with zooms, the instant feedback of digital, the time of a film - scanning workflow. And the intangeble, the enjoyment of using a view camera and ground glass, something that I found important.
This is a far more convoluted issue than the "pixel-peeping" of resolution. Like taking a good image...... one needs to take time to ensure that all important elements are in focus