I recently built a new computer with a core i7 6700K (4-core, 8 thread), overclocked to 4.6ghz. My old computer is a core i7 980x (6-core, 12-thread) overclocked to 4.2ghz. In single-core performance, the 6700K blows the 980x out of the water, but in multi-core, the 980x narrowly wins in benchmarks. My question is, which one is the best home for my Nvidia GTX 1070s? Or does it matter? The other system will run my AMD 290 and GTX 780.

The 6700K has 32gb of DDR4 RAM @ 2666MHz in dual-channel configuration, the 980x has 24gb of DDR3 @ 1866MHz in triple-channel configuration (not sure if this matters). With the 6700K, I run 3 CPU units (AVX) and 2 GPU units. With the 980x, I run 4 CPU units (SSE 4.2) and 2 GPU units. I've been running the 980x under Win10, but I switched it back to Linux yesterday evening because I can get about 2x the RAC under Linux with the same hardware (no idea why).

Thanks in advance for any input.

How many 1070's? I have had good luck with running 2 tasks per GPU (this seems to keep them more or less 100% utilized and gets me about 20% more work done than I would with a single task); since the OpenCL GoG app tends to keep a full core busy that means I use a full hex-core for my triple 1070 machines (and leave no CPU tasks running). I've been able to keep 6 GPU tasks fully occupied on an AMD FX-6300 which is probably comparable to your i7-980. See this thread for my observations on tuning my i7-970.

How many 1070's? I have had good luck with running 2 tasks per GPU (this seems to keep them more or less 100% utilized and gets me about 20% more work done than I would with a single task); since the OpenCL GoG app tends to keep a full core busy that means I use a full hex-core for my triple 1070 machines (and leave no CPU tasks running). I've been able to keep 6 GPU tasks fully occupied on an AMD FX-6300 which is probably comparable to your i7-980. See this thread for my observations on tuning my i7-970.

Thanks for the reply, Shaggie. I tend to run Linux on my machine with the 1070s, because I get nearly 2x the RAC vs running the same hardware on Win10. I run Arch or Manjaro (depending on which I felt like installing at the time, since they're very similar). I was getting right around 40k RAC on that system with Win10. It's well over 75k running Linux (this computer has been as high as 17 on the top computers list as recently as October). With your three 1070s, I bet you'd get into the top 10 if you ran Linux...and you'd only need to run 1 task per GPU because the Linux app is so much more efficient. I shave about 15 minutes off of a CPU task running Linux, too. Your GPUs will run hotter under Linux though, because manual fan control is difficult to set up (I was talking to someone with 4 1070s a while back and that's what kept him from sticking with Linux). If that's not a concern, you should give Linux and the optimized Nvidia app a try, you might be pleasantly surprised by the results.

This is a 980x ("extreme" edition), though, not the 980 or X 980 (both are 4 core, 8 thread and slower than the core i7 2600K). The 980x ruled the fastest consumer CPU race right up until the 3960X came out, and even that wasn't very much faster. It wasn't until the 5960x came out that Intel truly left the 980x behind and then they had to add 2 more cores (4 threads). Running mine at about 4.2ghz puts it ahead of the 3960x and 4960x and not far behind the 5960x at stock speeds, so this is still a monster of a system, especially when you consider it's 6 years old now.

I will definitely check out your thread though, as I don't believe a person can ever have too much information to draw upon. :)