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Is your 980ti oc? Is you 1080 oc?
1080 only 20% faster than 980ti
According to that result, he is only 7.5% faster.
Run with afterburner monitoring open and check GPU usage, maybe a bit of a bottleneck with cpu?? Try with a X45 OC
his physx score is always 3% or more less on his 1080 build so his combined wont be as good and hence his overall score.
Looking at just gfx scores he's now 15.6% faster. Still doesnt quite seem enough though.
Nothing wrong there then, was your core clock on the vga remaining constant?
Remember my 980 Ti was HEAVILY overclocked which added +1000 to the graphics score vs a reference model. The reference 1080 is ~22% faster than a reference 980 Ti.