@ Roey - my mosfet sinks also get very hot - around 60*C under Linx load. I also use a TJ-07, 2 x 92mm rear intakes (only one installed atm) and I use the 2 x 120mm top fans as exhaust fans - this helps keep the mosfet sink cooler, so in your case having no top fans will make things hotter obviously.

Since asus removed the onboard 'Power' temp monitor that the original rampage extreme X48 had (perhaps they thought people would freak out when they saw 50 - 60*C) I use one of the asus supplied temp probes and stuck it into the heatsink (wedged it securely between the fins) and connected it to the mobo - not ideal but it works.