This is not a simple question.

First you need to make sure your motherboard even supports these CPUs.
I had the e8600 and it worked quite fine.
Your Motherboard will most likely not support the Xeon, and prolly not support the Core Quads without a BIOS upgrade. And even if it does you need to make sure your PSU is up for supply the juice for it.

What you need to look is individual thread performance. Sadly Aion is not great at multi core support, so the fastest single core performance is the one you are looking for. The higher the clockspeed the better.

None of the above.

Save your money, get an AMD Ryzen or an intel CPU you know you can easily overclock to 4.5+ GHz.

Thank me later.

To be honest, yeah, that is the best direction to go with.