What are you brewing? Some beers benefit more from higher fermentation temperatures, some from lower. Remember that fermentation itself gives off heat. Your fermenter will be 5° to 10° warmer than the ambient temperature, at least for the first three or four days. A beer that you want to keep crisp and clean, pitched with a neutral yeast (1056, WLP001, US05, et al), would do very well in your basement. Pitch your yeast at 65° to 70° and put the bucket in the basement. By the time the wort starts to cool, fermentation will have begun. A beer that benefits from more yeast character, a wit or ESB, for example, would be very happy upstairs. If that were the case, I'd probably cool the wort to 60° or so, pitch the yeast, and let it come up to temperature as the yeast goes to work, but that's just me.
As has been noted, you can control temperatures fairly well with inexpensive tools. I use a bus tub, the kind used to clear tables in restaurants ($5 at your local restaurant supply), filled with water to keep my fermenter cool. Changing out a couple of frozen water bottles a day keeps the fermenter at 62° to 65° even in 75° ambient temperatures.
Chad