I've found, on my GPU, that switching to Direct Lighting/Diffuse kernel in Octane, instead of Path Tracing, increased speed from 0.5M to 1.2M on the same scene, same materials, and lighting situation.  That's more than double the speed increase, with very little noticeable difference in render quality.  I typically set the Direct Lighting/Diffuse kernel mode to 10 reflection, and 8 glossy bounces, and 2 or 3 diffuse bounces.  The higher you set the diffuse bounces, the closer your results to Path Tracing, at the expense of render time.  Try also the Direct Lighting/Ambient Occlusion kernel mode.  You'll see the render time cut in half yet again, at the expense of bounced light and scattering.  However, you can push the reflection and glossy bounces very high here, and still maintain extremely fast results.

I rarely use PMC.  ALthough it's optimized for the GPU, I've found it relatively slower than standard Path Tracing for the typical scene.  While samples do clear up faster for complex materials like glass or SSS, overall it seems to take longer to get the same results I get with Path Tracing.  It's handy when trying to solve caustics, or deep scatter, which can be very difficult to clean up with Path Tracing.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.