Motherboard selection for Crossfire + 2500k overclocking

Hi, Tom's hardware forums have long been my source of information on my previous builds. This is my first time positing so here is to hoping that you guys can help me out.

I am assembling a system for my gaming. The parts I have already almost decided on are

CPU: i5-2500k
GPU: 6850 (XFX or ASUS) haven't finalized yet
Ram: G-Skill RipJawX

However I am unable to decide on a motherboard as of yet. I need it to be able to crossfire later on when I can buy another 6800 series card. Also the motherboard should be stable enough to overclock the 2500k to respectable levels.

I am also gonna put in my sound blaster card in one of the slots. Would that be an issue when I try to go for crossfire?

The PSU / casing / hdd will be used from my existing PC so no need to purchase them at this point of time.

I was inclining towards these boards:
http://www.asrock.com/mb/overview. [...] me3%20Gen3
OR
http://www.asus.com/Motherboards/I [...] 8Z68V_PRO/

but frankly I am at a loss to compare the motherboards, most of the features are almost similar. My biggest issue was to find a board with good over-clocking capabilities for future with crossfire support.

I am based in Singapore so parts availability should not a issue.
Any advice will be much appreciated.

Cheers,
Joji