Multi-monitor (cloned signal!) question

I have only one game I'm aware of that uses OpenGL (Brink).

I run 2 monitors in cloned mode (for ergonomic reasons I won't go into
here unless really necessary) from my GTX590 to two separate monitors.
The nVidia drivers do advise that multi-GPU performance may be reduced
if I do this, but I've found that it makes almost no difference in
DirectX games.

However, in OpenGL, running two monitors cuts the framerate in half.

Questions:

1. Is there a way to overcome this? (I'm guessing not, and that it's
just the craptastic nature of open-source hardware acceleration).

2. Is there a way to set up hot-key (or otherwise convenient)
disabling of the non-gaming monitor so that I can quickly switch
between "gaming" and "work" modes?

Much thanks to any assistance.

Rin