Speed issues with multiple monitor setups.

I have a situation where I want to mirror a display on a second monitor with slight rendering differences. (So I have 2 windows from one app, on different monitors) I’m using a geforce4 ti4600 on win2k. Now, when it’s using the default nview stuff, I get rendering speed about what I’d expect, but when I enable the nvidia ‘Treat multiple outputs on an nView-capable board as separate display devices’ (Which would be preferable for usability - the second head is not next to the first head), the framerate halves.

Anyone know if theres a way around this?