The lower card GPUs are at 64/61 deg and upper are at 76/69 deg.  They are running with the OC switch in the default (non-OC) position to reduce power consumption.  With OC enabled one of the upper card GPUs likes to get up to about 90 deg, and the rig draws nearly 2 more amps (~7amps vs ~9amps).

Right now I am using the Koolance Exos 2 all in one cooling system.  Very easy to setup and nice design.  However, the Exos 2.5 (with 3 fans instead of 2) is probably better suited to dual 6990's - got one on order to see what kind of difference it makes.