gpu bottleneck not cpu bottleneck
you said it yourself, sandy i5 can fully drive 980ti, hence bottlenecked by gpu, not cpu
just because there is no difference in framerate (very small) does not mean extra threads dont or cant get used.
unlike you, i look at benchmarks with dual 980s. http://gamegpu.ru/test-video-cards/igry-2014-goda-protiv-protsessorov-test-gpu.html
sandy i7 is better than haswell i5 at same clock... in games aswell.
and xeon 1231v3 is also better than 4.6 4690k.
todays engines dont only use 8 cores (8350 easy example so you can see diff)... they even use 5820k and benefit.
oh, and just so you know how i5 can even be bottleneck,... 100% load on assasins c unity
also i am very tired of only me posting benches all the time