"Henry, I plan to scan for reproduction up to 50x70 fine art (ie a 10x enlargement from 5x7). All prints won't be reproduced at that size, but at least some will, and if buying a high-end scanner I want to be able to "scan once for all". "

You've probably already done this math but here it is again: For 10X enlargements, if your output device needs 200 pixels per inch for high quality results then you'll want about 400MB files from full frame 5X7. Thats about 2000 ppi hardware res needed from your scanner. I base these numbers on my experience with a Durst Lambda. When I make small prints I usually go to 400 ppi at desired output size but for larger sizes 200 gets the job done wonderfully as viewing distance covers any loss. (I only find this loss with the occaisional hard diagonal line in architecture, I'd say it would almost never be an issue with landscapes)

If the machine to do this is too expensive, you might try a scheme that covers 80 percent of your needs, a scanner that will give the quality needed for prints half that size, perhaps 25X35. I say "80 percent of your needs" as I suspect that most of your sales will be for prints this size and smaller, but I'm just guessing at that. I suggest this only because the cost and operation of the perfect machine may be quite high. Of course its your money so spend it as you please. I've always considered digital equipment purchases as necesary business expenses and simply buying the "absolute best" has never been an option for me, although I have dropped a bundle on expensive digital gear lots of which is now obsolete or broken and unrepairable. This stuff is NOT like buying a LF camera that might last two lifetimes.

I'd ask some scanner owners to provide samples of your film scanned on the machines you are considering, it'll be worth the small cost to prove that a given machine will do what you want. Here in Nashville, Chromatics http://www.chromatics.com has a 8000 ppi drum as part of their digital services. I'd use scans from that machine as an ultimate reference. (or similar machines in your area)

Jeff Moore, I'm in the Nashville area. Have we ever met?