In my quick research on the 3 models you gave me, the 2683 v4 es can be obtained for under $400 each if you're willing to bid on ebay. Otherwise, they were 500+ and then the 2695 would be in the same price/performance ratio. The 2697 is in another league as far as single thread performance according to passmark and the prices on ebay seem to reflect that too, often charging a premium: PassMark - CPU Comparison Intel Xeon E5-2683 v4 vs Intel Xeon E5-2695 v4 vs Intel Xeon E5-2697 v3
I got pair 2683 v3 CPU's (14 cores) and ASUS Mobo with All-core Turbo unlocked (14 cores @ 3.0Ghz). No rush in selling that, but if you're interested - PM me. I'm not using that to it's full potential anyway.