Thank you very much, man.
What about motherboard, will it be OK?
Yeah, I didn't reply to the mb part, I'm not sure. I'd suggest the cheaper one because system level OC has no effect on mining.
What happens though is that OC friendly motherboards have components rated for the extra stress, including better capacitors, more phases, better cooling, etc... Elsewhere I read about boards having issues detecting the 4th or 5th GPU and serious problems with more. Sometimes it's disabled PCI-e connectors when the adjacent is used, others is PCI-e related problems until you disable integrated audio and firewire or disable some power saving options ...
In other words, between those 2, I'd choose the cheaper one. If any of those 2 is actually a good choice for mining in the first place, that I don't know.
Still related with storage; if you intend to solo mine, you will need some extra disk-space for the blockchains. Otherwise 30 GB is plenty for a mining rig with OS and lots of of utilities installed.