Your sentiment is, imo, incredibly misplaced on getting 3/4 gpus... It's a PITA and just a waste of cash.
There are still plenty cheaper.boards that are as good as the ROG boards (giga soc/asrock ocf)...
This is pretty muc bang-on. 4 cards, you'd be making a mistake not going with X99, IMHO. You need the extra PCIe, especially if going with AMD cards since they use PCIe bus to communicate for Crossfire now, and no bridges.
With voltage regulation moved into the CPU, what EarthDog here says is pretty accurate...board doesn't matter much except for BIOS tuning for LN2 use. For 24/7, all that matters is the features you want, and slot arrangement for your chosen VGA config.
With 280's... the PCIe bit isn't as crucial, but only boards that have a PLX bridge chip like the ASUS MAXIMUS Extreme boards will work, since the max is three VGAs, and you get a 8x4x4 slot config with most boards, since the PCIe is in the CPU, and that slot support's not any good for multi-GPU. So you're choices are pretty limited..you got the Gigabyte Sniper board, the ASUS Maximus Extreme, or the MSI Xpower as your only options.
Move to X79 or X99, and that story changes.