From the testing I did with this I can say that you need a bowed heatsink or waterblock on 1155 and a less bowed version on 2011.

The reason being that the edges of the ihs are invariably higher than the center and it is the center that needs the contact most.

The normal springs one gets in a water block kit could do with being upgraded for stronger ones or if you feel you want to really get good contact pressure maybe consider torquing the nuts down onto bound springs.