My own .02 from experience:
1) It's extremely difficult to get a "perfect" LF film capture. First off, film flatness is an issue, second, precise focus requires that your GG is in perfect alignment with the surface of the film in your film holder. And film holders can vary in film plane by several thousandths of an inch. And then film rarely is perfectly flat in the holder.
2) 8x10 is even less accurate in the above respects than 4x5 but;
3) It is much easier to critically focus the larger 8x10 image accurately as it has more CoC tolerance to begin with; even more so with 4x5 compared to current 6x45 MF.
4) Example: When I had my Betterlight scanning back, I could "see" where a 0.5mm change in focus extension would alter the exact PoF from a 210mm lens at f11 from 100 meters down to 10 meters...
5) Glass becomes a limiting factor as you move up in format as well, and this removes a significant portion of the "4x gains" in film area from 8x10. My best 4x5 lenses rendered as high as I could measure them, which was around 60 lpmm centrally (arguably these lenses could be rendering as high as 90 lpmm, but I couldn't confirm that with my test equipment); by comparison my best 8x10 lenses were in the mid 40's with one hitting 52 centrally. Clearly there are exceptions here in both directions, but I think these are pretty "comfortable" resolution numbers to use as a generalization from the best modern LF glass.
6) By contrast, I own MF lenses that clearly still resolve beyond a pixel on my MFDB which has a 6u pixel pitch. 6u pixel resolution basically means the sensor is theoretically capable of resolving a little over 80 lpmm for a linear black and white line pair, or around 55 if you go with Nyquist.
My own "conclusion" on how many pixels it took to match each medium, assuming the best possible glass being used for all mediums, was ~~50MP to match a perfectly captured and scanned sheet of 4x5 and ~~100MP to match a perfectly captured and scanned sheet of 8x10. Corollary comment here is even when taking extreme care in my set-ups, I got maybe a 30% hit on the "perfectly captured" part for either 4x5 or 8x10. Not saying the other 70% were unusable, far from it -- just not "perfect." (I had a much higher hit rate with the Betterlight because it had electronic focus confirmation and was of course a perfectly flat capture plane.)
For comparison, with my current MF digital set up, I find my DF body's auto focus to be more accurate a far higher percentage of the time of the time than I ever was with a 10x loupe and a GG, and of course obtaining correct exposure is immediately confirmable. Thus, I'd give my current 60MP MFD set up a quarter notch over 4x5 most of the time and maybe rate it a half notch behind my best 8x10 captures. Of course as soon as you factor in convenience, the film solution drops way down the ladder for me.
In the end, my own opinion is if you want to deal with it, 4x5 and 8x10 film still offer a very viable solution for generating the highest quality captures.