mesured it with a thermometer with a little dab of Arctice silver on the end
its quite accurate, to within 3'c usually. i just tried playing Iront Storm (for the first time, i quite like it ) and about 15 mins into it the comp crashed, so i checked the temps, and the southbridge was nearly at 80'c
i am going to use the northbridge heatsink (with a corner cut off so that it fits snugly) with a fan mounted on the edge of my gfx card (its a gf fx 5950 ultra, it needs all the fans it can get, lol) when my watercooling for the cpu/nb/gpu gets here.
althought, without the heastink on the northbridge, it doesnt get nearly as hot as the southbridge with its heatsink. (dont try that at home kids, i kept my finger on it at all times and if it were to overheat, i had a heatsink that i had left in the freezer ready to slap on it to give me abough time to shutdown) maybe i will see if there is a way that i could secure a waterblock to the southbridge, the only thing that i'm worried about is the weight and pressure from the tubing, as there is no way of physically attaching a heastink without glue of some kind. :shrug:
hrm. i'm gonna have a think and a mess about with a load of random heasinks etc. and get back to you on this one.