Paul has put some great info on his site about the scanning software and Dmax:
Since Dmax is as important as resolution for B&W, I wanted to see what a new generation consumer scanner could do. To this end, I scanned a 21 step Stouffer step wedge - same density range as the 31 step, just steps of .15 rather than .1 - multiply my step numbers by 1.5 to compare with Paul's.
I used Vuescan and took the raw data file and adjusted the gamma in Picture Window Pro, then slightly adjusted the low end contrast with curves to better separate the lower steps. (Remember, this is a positive image, so these would be the highlights on a print from a negative.) This was scanned at 4800 DPI, then sampled in Vuescan by 6, to give a final file of about 20 megs. No other manipulations.
I think I have clearly useful data to at least 18, and perhaps 19. While you can see 20, I am not sure how good the data is. Since there is no detail to resolve, it is hard to say what this means for highlight detail, but it is clear that the scanner can resolve more in the highlights that I was assuming. You lose a few steps by letting the software scale the data. I am sure there is noise, but highlight noise on 4x5 is not a big issue to smooth out. (I did the same with Siverfast and the results look about the same - while I think the Vuescan file has a little better Dmax, that might be related to the extra steps I have to go through to process a Siverfast file since is not flat tiff.)
This is easy to do, and since there is no dmax test on the scanner test page, perhaps others would like to add their scanners. The Photographer's Formulary (www.photoformulary.com) sells the step wedge for a lot less than anyone else I found - $26.