What kind of temps are you getting? Monitor during benchmarks to make sure you are not getting too hot and it's throttling, and as asked before, are you running the latest drivers.
Tom's used the latest beta drivers, 352.90, for their 980ti testing.
You also have to take into account they run benchmarks on clean installs with no virus, scanners, or anything to take away any performance and use the highest CPU's, massive RAM, SSD's in RAID to take every single possible little bottleneck out, which gives a better idea of the GPU's power, but in reality, not something everyone can do.