I wonder if some of the conflicts about scanning resolutions and print quality arise from confusion about alaising and scanning. From what I remember about sampling theory, you have to sample at twice the frequency of the data you want to capture. If I want a 16 x 20 printed at 240 DPI, then I need a data file that is 3840 x 4800. This would be scanning a 4x5 at 768 DPI. Doubling this for alaising, I get 1536 DPI. If I want to put 300 DPI data down on the print, this goes to 1920 DPI. Thus in our thread about comparing 4x5 and 8x10, the 100 meg scan of the 4x5 was at too low a DPI to collect enough data to even get 240 DPI down on the print.
This would be consistent with the observation that good consumer scanners can produce 16x20 prints from negatives that are indistinguishable from drum scans, because a good consumer scanner can probably produce a good 2000/2200 DPI scan from a negative by scanning at 4800 DPI and downsampling. (DMAX and noise become a big problem for chromes.)
Above 16x20, the advantage of drum scans would become more obvious as the print increased in size. Having an optimum negative might push the best printable size with the consumer scanner up to 20 x 24. Of course, this assumes fine detail in the picture. Clouds over a pond might look the same in any size print. I think that is also why we see people saying that their 8 MP DSLR makes great 16x20 prints - it will if you have no fine detail and properly process the data to smooth out the pixalation.
Comments from some of our math oriented scanner mavens?