...I don't think Sigma Art whups average good DSLR lenses...various reviews fwiw confirm that Sigma Art are another marketing ploy...
Your opinion is of no consequence compared to actual measurements. My Sigma Art 35mm, 50mm, 85mm and 105mm lenses' performance far exceed what "average good DSLR lenses" achieve. Do some research at reputable, objective testing Web sites. Various squishy, subjective "reviews" you might have seen from Internet trolls mean nothing.
...I don't know what you mean when you say "even holds a candle to even the full frame files." What "full frame files" are you talking about?...
The full frame files from my D810+Sigma Art lenses, of course. Most APSC files are much smaller and less detailed, simply due to their substantially lower pixel content.
...Have you compared files from your 810 to any of the better APS DSLRs?...
Why bother when the difference in pixel density between full frame files and 8x10 scans is plainly obvious? I don't waste time on downgrades. Also, why would I investigate replacing an entire camera/lens ecosystem when only the most recent APSC DSLRs (introduced after my Nikon/Sigma kit was established) included sensors with more than 2/3 the pixels of my current equipment?
...Your introduction of 8X10 negatives into the discussion means something is wrong with that D810...maybe it's the Sigma lens...
There's not a thing wrong with either of my D810s or any of the Sigma lenses used with them. Apparently, some people are less sensitive to visual differences than are others.
...11X14 is far from the largest print from Pro-100, you should be able to get almost 13X19, which is vastly larger...
I've no desire to print larger than approximately 11x14 with my PRO-100, my Epson P600 or any other printer. Also, 11x14 is more than large enough to see the limitations of full frame sensors, just as it was the size where 4x5 negatives' limits became apparent in darkroom printing.
...Maybe you're using very soft paper? That's important. I think you'd be happier with something more like Canon's Fibre paper, which isn't expensive...
I've tried and rejected quite a range of papers with both printers. My current standard, with which I'm extremely happy, is Hahnemuhle FineArt Baryta Satin on the PRO-100. It's far from "very soft."