Tell us your specs and the plugins you're using. It will help us.
The slowdowns are usually blurring or distortion effects that require a lot from the cpu and the video card. If you're using Pete's gpu, you can try setting Framebuffer Textures to 1-Black, and disabling FVP. You won't get those effects, but you'll get a big speed up. If you really want those effects, try Pete's Soft plugin.
The slowdowns are usually blurring or distortion effects that require a lot from the cpu and the video card. If you're using Pete's gpu, you can try setting Framebuffer Textures to 1-Black, and disabling FVP. You won't get those effects, but you'll get a big speed up. If you really want those effects, try Pete's Soft plugin.