Thanks for the suggestions.
I've looked at the Asus X99 boards in the past, but I've heard mostly bad things about them. I've spoken with some experts recently, and they have recommended any of the Gigabyte and ASRock boards from their experiences dealing with X99 builds. According to them and many online reviews, the Asus X99 boards just consistently fail to pass muster when it comes to stability and quality control.
I initially had the MSI Xpower X99 AC spec'd, but I changed that to the ASRock X99 OC Formula a long time ago for the same reasons.
As far as GPUs go, I'm looking at MSI's Lightning Edition because of the heavy heat sink that is included on the card, the dual BIOS chips, the high marks from TechPowerup, and generally favorable public review distribution. People have reported stable overclocks in the 1445~1510MHz range with the factory installed air cooler.
I will most likely experiment with liquid cooling at some date in the future when I have the money to burn for that sort of thing, but I am happy to stick with a big air cooler for now. Going to go with the legendary Noctua NH-D15/S. I expect no issues getting up to a stable 4.00GHz with that cooler. Low maintenance, very quiet, and no chance of leaks, pump failures, or other nonsense until I am ready for that sort of stuff.
I'll probably look into SLI with either another 980 ti, or the new Pascal GPUs at or before the time I start building a liquid loop.
The case configuration I will likely be settling on will have factory support for three 4x120mm rads, and four 3x120mm rads. If I should ever need more support than that for whatever reason in the future, I can purchase and install a case extension that will add support for six more 4x120s, and five more 3x120s.
Nothing succeeds like excess. :3
Goodbye crappy toaster, hello shiny new powerhouse.