I noticed the higher T nightmare dungeons I do, I seem to get more ancestral, but do you guys know if the higher T difficulty scales the ilvl at all?

Im not sure. Also ive never dropped any ilvl 825+ and ive seen s/s of 840 ilvl, i wonder if they drop more in t90+

840 can be dropped by super unique monsters. 825 is max for regulars. super uniques have specific locations and only have 3 stat affixes. higher nm dungeons seem to drop higher stuff in general