There is some evidence (debatable) that lower bodyfat percentage helps partitioning a bit. But in addition, beginning a bulk from 15% or higher reduces the amount of time you can continue bulking before you become a fat slob. Most conventional wisdom suggests bulking from 10% until you hit 15%, then cutting back down to 10%. Personally, I have had success bulking beyond 15% but keep in mind that the longer you bulk, the longer you will have to cut later on. Depending on what bodyfat percentage you are comfortable being.
Eh, I guess that's kind of a non-answer. The important thing is... what bodyfat percentage would you ultimately like to be at?