I am in a very similar situation to you (the OP), but I immediately began with the idea of using NiceHash to sell hashing power and get paid in Bitcoin.  With a many year history of building (non SLI/CF) gaming rigs for friends and family (usually on 2-3 year GPU and 3-5 year CPU/platform upgrade cycles), and having a pile of leftover parts... many were good enough for the task.  As such, rigs that I now have running (all using Windows OSs):

1. Intel i5 7500, H270, 2x8GB DDR4, (1x) Nvidia 1060 6GB
2. Intel i3 4160, Z97, 2x8GB DDR3, (1x) Nvidia 1060 6GB
3. AMD FX 8320, 970/950SB, 2x8GB DDR3, (1x) Nvidia 1060 6GB
4. AMD Phenom 2 720 BE, 770, 4x2GB DDR3, (1x) AMD R9 270X 4GB
5. Intel Core 2 Duo e6750, P45, 4x1GB DDR2, (1x) AMD R9 270 2GB

6. (Waiting on full part availability for system, including RMAs) AMD Phenom 2 720 BE, 770, 2x8GB DDR3, ?

In the end, the GPUs are the only thing that truly matters.  (As for my setup, it is highly inefficient based upon electric & cooling cost to hashing power.  However, it is winter where I live, and the extra heat of the systems is being used... to heat.  In summer, the lower quality rigs will likely be shutdown.)