KLiK, not a bad collection of stuff there. All you need is a new board and some DDR4 memory, which is coming down in price and you can do it. I'm using a supermicro X10 board and got the ram second hand for a good price (at the time).

A.S.I. - I found the 2683 V3 on ebay for about $450-$500 but the clock speed is so slow that my 2680 with less cores does better than it's 14 cores. 16127 vs 18403 on passmark. So that would be a step down.
The other 14 core ones are, the 2695 and 2697. There is a pair of 2695v3 going for 1500 Euro or $1700 but bidding isn't closed yet.
2697s, are way more expensive, going for over $1000 each.

I found the guy selling 16 core processors, but they all seem to be sold and I think buying a pair of them may have meant a new motherboard which I don't want to do as they are are from the E5-4600 series. And the cheapest I could find was about $1300 on ebay.

So I think my dual 2680V3s are maybe even a bit cheap at $1000.