980 SLi >980ti >titan
the only real advantage titan has is more ram but i'm quite sure the gpu horsepower games will require will outpace vram requirements. even if you consider console ports the next gen of hardware is some years off and current hardware is limited in ram to i think about 8gb(not sure about this). hence ti over titan bu that's only if you're considering the titan.
ultimately, gpu horsepower is what makes a game squeal so, more the merrier. hence, cuda power(sli) over everything else would be my final suggestion.
imo too more future proof.
do you know what specific cooler master psu you're using?