I did some more research - this is what I was looking for, a RivaTuner graph with both temps & fan speeds...
In 2D mode, the fan spins @ 2,000 rpm (40%) compared to the gtx280, which does only 1,300 rpm @ 40%. In full load, the fan gets to approx. 2,700 rpm - around 60%, while my gtx280 fan only reaches 1,800 - 1,900 rpm (~54%) to keep the core hovering at 79-81 degrees.
So it seems that the fan profile is more aggresive on the gtx295 - but it makes sense, since in this case you have one fan trying to cool down two GPUs.