The 2550K will overclock far more on the stock cooler, because Ivy Bridge CPU's tend to have heat problems.
Even with water cooling, max Oc vs max OC, the Sandy Bridge still wins.
If performance is your main concern, go with the 2550K.
And the motherboard you're considering is ok if you're not going after serious overclocks.
Otherwise i'd suggest this one as the minimum.http://www.amazon.com/dp/B007ZYI5M4/?tag=pcpapi-20