About 11 fps with nothing happening, 8 when i have to fight someone. I've never ran into so many walls. This is all at the 640x480 resolution too.
Rain effects and fog always have a heavy graphics consuming effect, so for people with low-edge rigs, it will totally slow them down. Probably they will add advanced options regarding these effects eventually so people that can't handle them will have a chance at playing.
There is a certain constant lag with the new map. My Alienware Alpha is just making a constant stream of lag rather then huge spikes.