Hi,
If you wanted to save some cash you could just get the Gigabyte GA-870A-UD3 for £65.99 - it's the mobo I'm using for mining. It has two full length PCI-E slots and two small 1x slots.
You can actually use all four PCI-E slots for mining, even the 1x ones, you just need to use a PCI-E riser extender cable, 1x > 16x. Although if you are planing to put four cards with risers inside of a case it may be a bit of a squeeze.
Cheers.
Edit:
link to mobo: