Stay away from anything Gigabyte. The bios is horrible!! I spent 5 hours last night with my X99-UD4 to find out the fix was to downgrade the BIOS and shut off the "full screen logo show" in order to stop my boot loops and crashes. Now I have a strange issue with the VID on the CPU not being consistent through all cores which in turn I have to drive up the voltage to enable more voltage for the other cores. The MSI X99S SLI Plus was a decent board but had a strange cold boot issue every once in a while.
Probably a good idea to wait. Now I wish I kept my Z97-A/4770k setup.
I'm going to wait, but I'll probably spring for the Rampage anyway. I want to see "new, improved" DDR4, and I want to see upgraded micro-code in new production runs for the E processors.
Someone else told me that being a prudent enthusiast means choosing the right time to build and upgrade. But I had said much earlier that it is like surfing: you want to catch the right wave.
The new, improved socket-2011 will be compatible with the Broadwell-E chips. There is no guarantee that newer X99 motherboard designs will be appreciably better than those currently released. And of those currently available, I would think that BIOS updates may resolve any shortcomings. At least -- I would hope so.
So far, the prospects for the i7-5820K are reasonably bright. But if I build one, it will be my first custom-water-cooling experience. It's all going to be expensive: the motherboard, the DDR4 -- the water-cooling parts -- even the case if I have to buy a new one. I can wait another six months before I spend the money and go to work.