I've noticed that it depends on how vigorous the fermentation actually is. And it seems like the hotter it gets, the faster it goes, so the hotter it goes.
I've been keeping my fermenters pretty well controlled for the last three years or so, but even yesterday I noticed that my room was 59 degrees and one fermenter was chugging away at 66 degrees, while one was more slowly fermenting at 62 degrees. (Both are fine at those temps, so I left them there).
Broken Leg Brewery
Giving beer a leg to stand on since 2006