I'd never heard about microcode lockouts before - that Intel patent is quite disagreeable, lol.

I think few enthusiasts would go this route anyhow because Xeon procs cost substantially more than their (already costly) Core counterparts and are not widely available through commercial channels.

Most Xeon parts are slower than their Core counterparts, too. And they also tend to overclock very poorly, I'm told.
A SuperMicro C7X99-OCE is a premier overclocking mobo in the server world, but it falls far short in this regard when compared to the beastly overclocking available on an Asus X99-R5E.

That patent has nothing to do with ES processors POSTing due to a microcode lockout. It cites a mechanism that allows manufacturers to lock ME or microcode updates to prevent inadvertent updates that may impact platform stability. Must be "supposition Friday" today in some parts of the world...

You have to experience the lockout to know about it. The microcode update would be pushed out with a BIOS update for the board. So you'd be stuck on an older build without having the option of updating to newer builds that may either patch platform bugs or add support for new features.

The reason I know that the 16 core parts work is because I was the person that passed Fugger an updated beta build to disable individual cores so that he could bench the CPU on Ln2 (people are given them to test or they purchase on illegally ebay, hence my post above).

-Raja

I went for the Xeon E5-1680-3 proc. Mine is some sort of SuperMicro OEM rebrand, but this isn't an issue. My IT contact informs me this proc was originally purchased through NCIX, hope that doesn't mean I need worry over the mysterious "microcode lockout" issue mentioned above.

Looks like win-win so far. This proc actually has slightly better specs than the i7-5960X, I almost wonder if it's just a higher Intel bin/package of the same die (but I don't intend to find out with a costly de-lid or two, lol). Stock performance speed is just barely faster enough to be noticeable.

I am highly pleased that it has a robust iMC - all of my troublesome/finicky 8x8GB DDR4-3000 "incompatibilities" just magically vanished - full speed, out-of-box voltage, plain XMP, no manual tweaking needed! I'm not sure if it's because Xeons as a group are better in this regard, or because my particular E5-1680-3 is better (and is designed to address up to four channels, up to three DIMMs per channel, up to 768GB max RAM), or because my particular i7-5960X might have been weak. Happy to confirm that it wasn't the R5E mobo.

Still running my customary self-imposed 24 hour stress test, looking good so far, and it hasn't exceeded 72C under full load (while my old proc peaked at 79C with the same cooler).

1) Before I play with overclocking possibilities - is the extra Asus OC Socket functionality compatible with Xeons? I realize I can disable the feature if needed for unexciting Intel-spec LGA2011-3 compatibility. But I suppose it would've been wiser to ask beforehand, lol.
Yes, the OC Socket seems to work perfectly!

2) I also realize the R5E mobo isn't specifically engineered for the server market. But do the BIOS workarounds/fixes/errata identified in the Intel Xeon E5-3 Processor Specification Update tend to be fully implemented? (Aside, perhaps, from irrelevant errata involving ECC, RDIMMs, etc.)

3) Last question (I hope). Will the presence of a Xeon activate any server-style complications in my TPM? I basically use it only as a Windows BitLocker hardware token, I know it can do a lot more but I'd rather avoid the configuration details I suspect are involved in overkill Enterprise security.
Yes, a few more TPM-/Security-related options appeared in the BIOS.

22c/44t would be a nice upgrade. Provided the socket is the same, I don't know why a Xeon V4 wouldn't work after patching the BIOS with the relevant microcode. I upgraded an Intel i7-965 Extreme 4C/8t to a Xeon X5690 (6c\12t) on my Rampage 2 Extreme mobo. Big improvement. When my i7-5960X gets crusty then I'll replace it with a Xeon v4. However, it is not there yet.