...Database to reliably be able to know your win rate? (BB/100)

How many hands do you need to even out the rushes and cold streaks to know how much you ACTUALLY are making (or losing)?

I'm a Limit player, not NL.
I have a DB with 13K hands and even this many doesn't seem enough at all to draw
any real conclusions from...(but then again, I just got PT 2 days ago, so I have no idea)

Thanks,