I won't be so melodramatic as to compare naming your baby "Six" to assigning slaves and prisoners their numbers, but your entire message and goal here seems quite pretentious and self-indulgent to me. You can be unique regardless of how common your name is. I could name my kids "Apple" and "Sprocket" without any fear of there being other kids with those names, but does that make them *good* names? Not necessarily.
Basically, if you don't name your daughters things like Sarah
, etc, you're pretty safe. Clearly, the decision is yours, but "Six" smacks of effort.