For 3+ gpus you need the extra lanes of the x79 boards but I'd struggle to recommend anything more than a 3820 even then - a 3930 just has extra cores which games don't use.
There is very little to choose from between the z77 boards - they all overclock really well (better than you will ever want to put enough volts through to test)
The MSI range are great all rounders and very energy efficient. I'd get a GD55 for an i5 and the GD65 for overclocking an i7.
The ASUS maximus gene is a fantastic little board which fights on the same footing as the ATX boards.
Thanks I need a board with a slot config of something like this: 16 1 1 16 1 16 or something so I can easily run 2 sapphire 7970 in crossfire on air with plenty of space between them...... GD65 maybe?
Only thing that stops it being perfect is the newest BIOS which locks down the core voltage from within the UEFI. You can work around it, it's just a little frustrating.
I'd suggest the gigabyte z77 ud5h ,the asus maximus v gene or the msi gd65 !!! All the boards are awesome when it comes to ocing but the maximus has better onbord audio !!!