My understanding is that with the change to GB on the Black, the OB runs much better than it did on Froyo, speed and bug-wise.
Regardless, the Black already has a LOT of work done to it. Having GB and some time on it before we get it, it will be pretty good anyway, but I suspect roms and such will be flowing quite soon after it launches. Rodimus for the OV launched the day after the OV officially was released, Stock + Xionia launched a few days later, Aphrodite about a month after that. The Black will be similar.