I am using 1080's not 1080Ti's, as I didn't want to spend too much up front right now. I have 1 more card slot to fill or replace the 970.
I wanna be frank, as far as mining is concerned, there is a world of difference between the 1080 and 1080 TI...the latter being much better suited for mining crypto coins for a profit (at this point in time). If you bought ur 1080 for gaming, and wanna use it to mine on the side, perfect..otherwise, it's the wrong card in terms of efficiency (at this time) for mining.
as always, please feel free to correct me as i'm almost sure there are other coins that i'm oblivious to.
Over here in the UK at least, you pay over 40% more for a 1080Ti compared to a "regular" 1080. There's no way the Ti hashes more than 25-30% faster than a 1080 (and even that's stretching it). So even if the Ti's faster and possibly a tad more efficient, the price difference just kills it. For me at least.