I only did a couple tests:
CPU: 8:56.96 (disappointing, but an older CPU, so I guess it is what it is)
Default GPU: 1:49.79
512x512 GPU: 1:23.22
Was really disappointed that my GTX970 was only .21 seconds faster than the time noted on the benchmark of 1:50 from a GTX 770. Two generations should make the GPU quite a bit faster. I guess it could point to the differences in the CPU as far as whatever is happening on that side (my CPU was at about 40% during GPU renders, so something still happening there).
Going to wait a year, then will pick up a new overclocked box with a newer processor (kaby, or whatever is out) and a GTX 1070 (most likely, as the price difference between the 1070 and 1080 is a bit steep). Get some water cooling on the bad boy, and do some faster rendering.