Also if you are using a cpu make sure you have dual channel memory for a big boost in hash rate. I have not tried it with a quad channel setup but I have a hunch you would see some performance boosts.
CPU-only
Yes memory bandwidth is usually the first bottleneck, secondary L3 cache size and finally - CPU frequency
Here are some GPU benchmarks for anyone that is interested, I ran mine on linux with a power limit of 95 watts for a GTX 1070 so you can get more hash with full power.
FYI GPU mining has been around for at least 6 months from my research.
Benchmarks https://pool2mine.com/bench
I'm running a few Xeons (E5 v4) 2.0-2.4kH/s per 110-150W (full system power consumption) also hacked a few low powered Intel (Core M) devices at 400-450H/s at 9W power consumption.
Those numbers beat any GPU.
I have also seen benchmarks on Intel gen 8. and AMD Ryzen/TR that can do even better than that. None the less RTX data is yet to come.