I actually never saw a single 1080Ti running without crashing with mem above +500. Most of them have problem with +400...
OTOH , the only 2 GTX-1080 (Not Ti) I have can run with +700 without crashing.
with equihash: -My OC Strix supports +130 Core, +1020 Memony -
-My OC Aourus extreme extreme water: +80 core, and really little OC in memory
One thing to keep in mind - some cards have a FACTORY memory overclock.
I've seen Factory memory clocks on 1080ti models anywhere from 10000 (effective) to a hair over 11000 (effective), which would be actual "base" clocks from 2500 to 2750.
A card that STARTS at 2750 isn't going to do +500 as easily as a card that starts at 2500....
EWBF in my opinion is overall the best ZCash miner, but Claymore is very close - I prefer the "configurable" fee option, as I think Claymore's 2% is an excessive ripoff especially now that his miner is NOT the undisputed hashrate leader.