Are you referring to framebuffer textures? According to what I found here, the level of three uses the CPU power and the graphic card power to enable some effects (otherwise it emulates some, such as most summoning and spells). Therefore, CPU power will determine this a little.
You mentioned this not happening in the past, so assuming it isn't hardware related, have you defragmented your hard drive? I notice you have the latest nVidia drivers. Sometimes, newer drivers can have a worse effect on cards older than what it's intended for. How long ago did this use to work fine, because those drivers are fairly new, meaning if you didn't have then last time it worked, you may want to try reverting to older drivers. Try other plugins and or settings as well.
By the way, I never saw any slowdown at all playing any Final Fantasy game on the PS-X.
You mentioned this not happening in the past, so assuming it isn't hardware related, have you defragmented your hard drive? I notice you have the latest nVidia drivers. Sometimes, newer drivers can have a worse effect on cards older than what it's intended for. How long ago did this use to work fine, because those drivers are fairly new, meaning if you didn't have then last time it worked, you may want to try reverting to older drivers. Try other plugins and or settings as well.
By the way, I never saw any slowdown at all playing any Final Fantasy game on the PS-X.