I like mine around 64%, but I keep inching lower, too.
I find that the richer, more full bodied, dark, long finish maduros taste better to me at around 65% or a little wetter. To generalize, nicaraguan stuff.
CC's and dominicans I like dryer, 64% or a little lower.
Like I said, I keep inching downward and watching the results, but the real rich, thick, strong stuff I like a little wetter.
The airier, spicy, and fragrant stuff I enjoy better dryer.
That's just my observation, no real studying about it.
I definately like my anejos and blue band o's and El Originals at around 68% or so. As wet as I can get them without screwing up the burn.