Your pickup height is 100% dependant on what YOU think sounds best. What I do is start out by adjusting the neck pickup about even with the pickup ring and then adjust (almost always a turn or two down) until my tone is right where I want it. Once I have the neck set, I adjust the bridge pickup to balance with the neck. Most people do the bridge first, but because my neck pickup tone is so important to me, I adjust it first.
It is worth saying that BKP's are EXTREMELY sensitive to pickup height. A half turn in either direction can be the difference between being right where you want it, and just a bit off. It may take you a while, but you will find it.