Won't make a bit of difference between 64 and 50degF for a couple of months. What's far more important is that it's at a stable temperature, as temperature changes can cause the carboy to pull in outside air as the temperature drops.
It's true that cellar temperatures are better for aging, but the difference you might see is over years and not months. The effects of aging happen faster at warmer temperatures, but also degradation. So if you want to put up some bottles for several years to see how they develop, keep them in your cellar at 50F. But for conditioning for a few months in secondary, there won't be a meaningful difference over a couple of months.