i have both 1070 ti and 1080ti rigs and i would rather run more 1070ti's due to lower cost the hash extra from the 1080ti's doesnt make a sinificant enough difference to justify the extra cost .
also i wouldnt mine eth atm there are way more profitable algos to mine right now there are lost of equihash forks that are almost 20% more profitable than eth mining right now.