I did a little bit more reading. There is a 2697A v4, which should be 2.6Ghz 16 core, that is a step up from the 2.6Ghz 14-core 2690 v4... 2697A v4 appears to be going around $40, I could swing it, obviously the value prop of a $21 or $22 2690 v4 is superior but hey i'll still take 16 cores over 14 cores for 20 more bucks... Now the real question I suppose is deciding between these Broadwells and the Haswell 2600 v3 CPUs with potential for BIOS hacking to unlock 3+Ghz all core.
Issues I'm aware of so far for the latter approach:
- Not sure how e.g. AVX workloads would work... it sounds like further tweaking would be needed to avoid that being a catastrophic power limit throttling situation. Unclear if solutions exist, although this post seems to indicate this isn't a big problem? I'd want to have a clearer answer on it...
- v3 only goes to 2133Mhz DDR4, only way to speed it up is with BCLK OC (v4 does 2400)
- Compute per watt surely suffers more at 3.6ghz
I'm probably going to make the call at this point that since I already have other faster machines, that the stock configuration and boost behavior would probably suit me well at the end of the day so I should just do the CPU upgrade. I did some compatibility lookups and it's not clear that 2697A v4 is supported in the gigabyte X99P so what i'm gonna do now is order a $22 2690 v4 and a $50 2697a v4, yes the 2697a v4 can be had for closer to 40 from aliexpress but I'll give $10 extra to an ebay seller to get it in one week instead of 3 weeks.
Edit: Cheapness prevails. I'm gonna just order two 2690 v4's