I would never buy a CPU off of ebay.
I've already done it and it was well worth it. I've
linked this before way back in April, but here's a great reddit thread on this:
https://www.reddit.com/r/Twitch/comments/47bzdc/budget_friendly_secondary_streaming_pc_guideThat said, this is not ideal for a gaming rig (unless your current rig kinda sucks, and even then, you can do better for
gaming for the money unless you already have the motherboard). This is an encoding rig. Or whatever else needs a lot of CPU cores, which doesn't mean gaming (gaming needs single core speed and mostly tops out at two cores).
Although, it seems that Overwatch is more threaded than most, and Star Citizen is going to be highly threaded, and this may be a trend going forwards, so there's that. Also if you intend to stream via OBS to Twitch, you could do a lot worse.
Anyways, the CPUs are the easiest part, the hard part is finding the motherboard for a palatable price. Once these CPUs got dumped on the used market, the motherboards got bought up. So if you intend to do this, get the motherboard first, CPU second, or don't bother. Look for people upgrading their X79-based systems and not realizing the X79 motherboard is still valuable.