The capped [bzw2]turnstile[/bzw2] attendance for PAX Prime is 70k (so ~23333/day on average) over the 3 days.
For PAX East 2011, they capped the turnstile attendance at around the same amount. For PAX East 2012, they said they would be increasing the capped capacity by about 20%. The BCEC can legally /hold/ around 100k turnstile over 3 days at this point, for a show configuration like PAX.
Physically, the BCEC has 2x the available Expo space that the WSCC has, and about 1.5x the theater space.