Wow what a wall of text ^^
So let’s get started:
Mobo could be changed to a MSI X99S SLI PLUS just a suggestion since I don’t use the 2011-v3 platform.
One of my concerns would be power, if you use two 290x and a hex core that will be very close to 750W max power draw without ram, fan and mobo chipset.
Probably you would run safer with a 1000W PSU
Greez
Ryx