I've already seen that FAQ page. My friend with same Nvidia 970GTX also have the same report. Compared with my iMac 27 mid 2011. My PC ( latest 6 core overclocked at 4.3ghz with 970gtx) isn't really much faster. So, I suspect GPU rendering might not be working properly.
Check OpenGL support: Failed
Vendor: NVIDIA Corporation
Version: 3.3.0 NVIDIA 350.12
Renderer: GeForce GTX 770/PCIe/SSE2
LanguageVersion: 3.30 NVIDIA via Cg compiler
Same Problem here...
Reread the original post. The GTX 970 passed, your 770 did not. It's not the same thing the OP is pointing out.