Ohh, i thought E7-4870 was top of the line? Cant see a better one in this list: https://ark.intel.com/products/series/59139/Intel-Xeon-Processor-E7-Family - Care to share your knowledge? 
Well now I feel like a dummy. I saw E7-8870s in the list before and thought it would be more of a boost than just double the accessible RAM which won't do us any good.
8870s can address 4.1TB while the lowly 4870 can only address 2.05TB I don't think that will give us the kind of performance boost we are looking for. I guess next time I'll make sure to check the specs instead of just going... Ooooh bigger numbers, has to be faster right? Found 4 8837s for 35 shipped, they are on the way... LOL
Cache is the most important factor here, mining cryptonight with xmr-stak. The configuration of the miner should be based on the amount of cpu cahce available. Each miner thread needs 2Mb of L3 cpu cache.
For the E7 family i made this formula to estimate cryptonight performance:
13 * corespeed in ghz * (amount of cache per cpu / 2 ) * number of physical cpu's * = Totalt H/s running one thread per 2MB cache
For me:
13 * 2,66 * (24/2) * 4 ~ 1650 H/s
one thing to also remember is there is a big difference between the E7s and the E700s and X7000s (which are the most common). The E7 series comes with AES-NI while the previous gen does not.
So theoretically which cpu should be the best one for cryptonight? As well as which is best bang for the buck?
Best bang for the buck would have been that $250 mini pc I posted
Actually though, best bang for the buck is always changing with these old xeons. You just have to scour ebay for the deals. Ideally though you would want Westmere or later. The E7-XXXX V1 is a Westmere, the next gen is Sandy Bridge with the v1 E3s and E5s, then Ivy Bridge, etc. Just make sure the processor you are getting follows the format of E7- or E5-. As someone else mentioned, the L3 cache is really the determining factor as to how many threads you can run. So the best bang for your buck would be to find cheap xeons with giant L3 caches. Personally I would search out the v2 and v3 E5s as the cache can go all the way up to 40.This is a great article with benchmarks that explains it better than I can: https://www.servethehome.com/monero-mining-benchmarks-cpu-mining-amd-ryzen-7-systems/
Also here are benchmarks in a list format: https://forums.servethehome.com/index.php?threads/monero-mining-performance.12116/
