I'm not sure what's causing it, but there is an extreme inefficiency somewhere regarding B site. I play at 220~ fps in a Casual but every now and then I get insane FPS drops down to 60~80 or less in & around B.

From what I see it most commonly happens when I'm positioned around the mini-fish pond and looking towards the big aquarium; on a Local/Offline server with no bots I get 300+ fps, but standing in the "CT Corridor Down" hallway looking towards the fountain I have 210 fps...if I recall correctly, this is the passage that's usually affected by the huge FPS drop.

The drop itself doesn't usually last for more than a second or so but it adversely affects the gameplay of an otherwise beautiful site.

It seems relevant so I might as well include: I play at 1920x1080p fullscreen with Multicore Rendering Enabled, and all other settings at their lowest value.