The clocks on the 7980xe are much higher to begin with, so out of the box it is a much faster performer. Even with the microcode hack the 2696 cannot compete with it.
Here's the feature comparison between the 2:
https://ark.intel.com/compare/81061,126699
The 7980xe has higher TDP so there should be more room for o/c compared to the 2696.
The 7980xe has 44 PCI lanes vs 40 on the 2696.
The 2696 has ECC support while the 7980xe doesn't.
The 7980xe has AVX-512 support while the 2696 has up to AVX2.
The 7980xe is 1P only while the 2696 is 2P (so you can expand your system by adding a 2nd cpu in the future).
The 7980xe is around $1900 so it's almost double the cost of the 2696, so even though they are not that much different, the cost is still substantial.
I'm currently running an i7-870 from 2010, so it's about time I upgrade, but still indecisive as to where I want to go. The 2696 platform is a bit old now, but the motherboards are still very capable and there is great choice, so that's not the issue.
I'm also hesitant to go with the 1950x Threadripper as it is a glue-job (2 cpus under a single package) so there are drawbacks which are shown in benchmarks. But the up-side is that it provide 64 PCI lanes.
I think i'm over-thinking all of this, too many options.
My goal is to setup an Unraid 6 server running 3-4 VM's, Emby, and of course NAS.