Diablo 3 is a worthless game for benchmarking. I run it better (in most cases) on my newer-generation 4xxx i3/860m than I do on my 3xxx i7 with a GTX 780. My i3 is a lower clock T-series, where my i7 is a K-series.
I have found that, in most cases, dropping the sound channels on D3 is about the best way to get performance gains. Sounds crazy, but works.