[NAME]​  If you are going to the effort to refurbish I would not get anything less than the i7-4960X . . . or just keep the CPU you have already. Looks like that i7-4960X goes for about $135 - $160 used on eBay for 100% positive feedback sellers with substantial sales volume.
There seem to be quite a few CPU options for the R4. Thoughts?   :)
Aurora R4, CPU options