The thermalright Ultra 120 can perform better than the XP-120 about 4~5 deg.C at load . No doubt about it . 

For me I will try to use the the Noctua NH-U12F  with an Noctua A.L.N.A. ( Ultra Low noise adapter ; bundled only with NH-U12F )which only generate  about 7db~ 8db and still would achieve about 95% efficiency for the cooling operation . 

For me the extra 4~5 deg C won't kill your CPU . Unless your CPU is running at something like >75 deg. C . 

I bet there is NO fan-cooled HS that can beat the Noctua at this noise level .
NOT even the Ultra-120 with fan .

Again ppl looking at the best cooling solution performance nowadays should look to a
water-cooling system NOT a fan cooling system . Buy the water-cooling
HS from Zalman / Thermaltake and they will beat the daylight out of MOST 
of the fan-cooled HS now available in market this include their own brand , Zalman , Thermaltake ,  Thermalright , or even an Noctua .

I believe  ppl who want to buy a Noctua have already understood that they are setting up a ultra -Low noise system and still achieve the optimal cooling effect
for their CPU .