Nouveau driver and GPU temperature

Since installing 11.4 on my main desktop machine I’ve decided to go with the Nouveau driver for my GeForce 8600GTS card and I’m more than happy with it: fast, smooth, and supporting not all but the most important (to me) Kwin effects. But there’s one hair in the soup:
the system temp plasmoid, using lmsensors, gives me much higher temps than I had under 11.3 with the proprietary NVDIA driver: GPU 75-79C, CPU 55-61C (almost critical for my Core2Duo, which is located above the video card).
Has anyone else experienced that? I’ve installed nvclock but it claims not to be able to adjust my GPU fan speed, which it says is 100% anyway (don’t believe that myself, too quiet for that).