Lots of new options nowadays so I really suggest you forget about the old servers you are talking as they are not good at all for gaming.
The old server workstation I'm talking about would have a CPU that has 4 or 6 cores, 3.1 to 3.6 Mhz, 10 MB cache ... hyper threading and AES NI ... that's all I "need" from it. The gaming is secondary. The mobo will accept the latest GPU, but that would cost more than the rest of the system combined. The system I'm looking at will come with 1 TB HDD (I'll add the SSD later) with space inside for a few more drives, 64 GB of DDR3 ECC RAM, Gigabit Network 10/100/1000, Integrated HD Audio, 4 X USB 3.0 Ports, 5 X USB 2.0 Ports, FireWire Port, and half a dozen SATA ports inside.
It would cost me about $600 USD equivalent, shipped to my house.
So, it's not the best for gaming, but it's more than enough for everything else I will use it for, including whatever cryptocurrency / bitcoin related projects I have. It will run Starcraft fine. It might not run the latest Assassin's Creed or whatever game came out in 2016.
I did some testing, ...
Mine takes about 20 to 30 minutes, but I'm still using a HDD, not SSD. Old laptop with Core i5. (probably 4 cores, or 2 cores with hyper-thread.)