I have an AMD Phenom II 955 (an admittedly old-ish CPU) and a GTX 780. My performance is all over the place, really. In 1v1 summer maps, I generally get about 40 FPS before all the action starts. In the mid-late game, I get around with consistent drops to the high 20s. In large team games, my framerate is pretty awful. I get 20s-30s, with pretty constant dips to 10-15 when there's a lot of action, especially on winter maps. I play on a mix of low-medium settings.
Interestingly, I get 50-60 FPS if I watch a replay with the UI disabled.