OK, I'd go 1080 Ti
Loving my
EVGA 1080Ti FTW3 Hybrids SLI does Not always work as planed -- depend how well your software is optimized to scale it correctly and with which Nvidia driver.
Newer Nvidia driver is Not always best
In my experience with other software, you will never hit the theoretical max of SLI ---> One 1080Ti will work better than SLI 970
See my signature "Nibbler", I have 10 series Titans also, get the Ti --> unless the software Mfg tells you otherwise
Your member name make me want to go back to Cayman and do some more diving