Now having a $3,000+ budget for a build, is not a bag of peanuts. The question in my mind arises, why are you, for THAT kind of money, considering a hack, as 3K also buys you the base (new) MacPro. You'll get support, you get warranty, and even if you use it for 2 years, you probably get like 2K or so back if you try to sell it, maybe more. I would rather think that that is not something you should disregard lightly. But you were thinking about keeping it for 5 years. What's a hack worth in 5 years? A few hundred, MAYBE. Nobody gives much anymore for a 5 year old processor, or motherboard. Maybe as a complete system you can get some money but you can't sell it as a hack. Or, I would be careful to say the least!
And what is a 5 year old Mac Pro worth? I'd say at least 1000+.
So, money-wise and performance-wise, the i7-4770K and i7-4930K and i7-3930K are top pick and the 4770K basically not far behind (cpu benchmark 10380) for $320. The other processors score higher(3930K scores 12163 and the 4930K scores 13354) but for prices around $570. As I take it from the comments, the setup is not an easy feat. The recommendation (Buyers Guide) is to not use 4th gen 4930 or 4960 as there is no support for them yet. Maybe there never will be. The E5-2630 is recommended and is around $630. If anything, then that you should consider and check out the board if there have been builds with it.
The GA-X79-UP4 or 5 cost around $300 to $450 for the UP5.
So, that could work, but there are some warnings. PowerManagement doesn't work out of the box. So are you willing to spend time and do you have the skills and determination to see this through...?
If I take the Xeon's and use the low end specs and prices (E5-2630 for $630 and UP4 board for $300) you spend $930 for that.
A 4 core i7-4770K costs around $320, a GA-Z87X-UD5H around $200, so that is $510. That's about $400 difference.
I would check if it is possible on the board but the Z series normally do support this, but stick in two EVGA GTX760 for $260 each, together with board and cpu you are talking about a bit over $1000.
Together with the other parts, say another $1100 as in your list, you'd be looking at around $2100 to 2200. And you will have power management working.
FCPX picks the presence of these two GPUs up as well and performance increases with at least 50%.
My recommendation would be GA-Z87X-UD3H, i7-4770k, two EVGA GTX760's. The board does support SLI and OSX has native support for it. Instead of spending a ton more, and walk into a headache if not nightmare, I'd choose this.
Happy building.
