To the OP:
The best 8x10 lens will generate maybe 30 LP/mm at the corners -- if you're lucky -- and closer to 50 in the center. Even tranny film like Astia can resolve 90 line pairs, so it is doubtful film will be your limiting factor with 8x10, your lenses will be. (4x5 is a different story -- LOT's of 4x5 lenses will do over 60 line pairs.)
Anyway, carrying on the math: 30 line pairs per mm is roughly equivalent to 760 per inch, and generating 760 pairs of lines per inch requires 1520 dots per inch. So, assuming you scan an 8x10 sheet at anything over 1520 DPI, you are probably at the maximum for the media. 8x10 at 1520 DPI equal roughly 12,000 x 15,000 pixels or 180 MP. Of course this is a theoretical limit, and in practice so much goes against you in generating a perfect 8x10 capture -- wind, vibrations, motion, lack of perfect focus, inability of film to be held perfectly flat, etc, etc, etc -- that I would say it's safe to assume more like 1/2 to 2/3rds that in the normal best case, so I'd call it 120 MP practical effective digital comparable in the best case, and maybe more like 90 MP in the average case. Either way, it is clear that 8x10 will rule the ultimate resolution roost for at least a few more years.
But from a practical standpoint, 60 MP is not all that far removed from 90, so we are getting pretty darn close with direct digital right now... Factor in the cost per sheet to shoot, process and drum-scan 8x10, and even the best digital back starts to look like a very economical option. Add in the workflow convenience for direct digital, and it's pretty tough to dismiss it in favor of large format analog...
PS: Yes, I have owned, shot and compared them all. In a real-world comparison, a perfect 4x5 or 8x10 capture (they are virtually indistinguishable at 40x50) when perfectly printed is an incredible piece of art. The problem is, for the reasons mentioned above you rarely have a perfect LF capture, and even more rarely get it perfectly scanned and printed -- so it becomes a numbers game. On par, you will have a few frames from LF that are superior to your best high-resolution digital frames, but on average most of your direct digital frames will be technically superior to most of your sheet film frames. And you'll definitely have more digital frames to choose from after any given shoot...
My .02,