What ring game win-rate is sustainable?

I've been on a major heater as of late. After a few failed forays into 25NL, I've finally found a home at 25PL. I'm confident that I'm playing these stakes profitably, but I'm just wondering what my true win-rate is, and how much stock I can put in my current win-rate after 10K hands. What about after 20K?

Now I know this is an incredibly subjective question. It depends on table selection, playing style, tilt, etc. This month, I'm soaring at a presumably unsustainable 13.5 BB/100. So, I know my true win-rate (assuming I continue playing at the same level of ability) is lower, but how much lower? How many hands would you need to be able to make a fair assumption of your actual earnings. Or, stated another way, at what point did you feel confident in your win-rate for any given stake?

I'm asking, because if things continue going this well, I will be staked for 50NL/PL before long. But, I need an honest and fairly reliable assessment of my hourly rate at the current stakes before I even think about moving up. For the record, I generally play 4-5 tables at a time. I have done more, but feel that my game suffers with more than 5.

I think realistically 5BB/100 (10bb/100) is about as well as you can expect, although there have been claims that double that is the top rate.

Yeah, I thought it must be somewhere around that. Guess I got a downswing in my future.