I think consistency is more important that a specific number, I wouldn't want to subject it to 38 degrees for 2 hours after being at room temp. The idea is to maintain a specific temp with slight adjustments to not shock the yeast.
just my opinion though, take it for what it's worth but is your basement colder than upstairs? maybe that is where you should ferment at.
On tap: #79 Berliner Weisse 1.030 9/20/12, Flanders, Barleywine, Wild Blonde (1.045 blonde hopped up and fermented with WLP644), #80B rett Saison
Fermenting: #82 Galaxy IPA, #83 Black IPA
Aging: #67 Bareleywine 1.116 11/07/2012, Flanders 2 batches 1.056 and 1.060 12/12/11 and 3/26/12, Kriek, 1.052 12/11,