Poor Nvidia GeForce 7800 performance with dual monitor setup

I just purchased a Asus branded Nvidia GeForce 7800 GTX. I have a dual
monitor configuration, something I've had with several video cards now
(GeForce FX 5800 and ATI X800, and now the 7800 GTX).

The problem is with the 7800 GTX whenver I have the second monitor
enabled (not dual screen, but I extended my desktop to the second
monitor). The problem is I get very slow performance.

For example I installed the new demos's for the 7800 (Mad Mod Mike,
etc...) And the thing plays like a slideshow.

If I disable the second monitor, it plays fine.

What the heck is going on? I never had this problem with either the FX
5800 or the ATI 800 when I played demos, games, etc... that were
available for those video cards.

I have the latest drivers installed (released Sep 2, 2005) Version
78.01

Any body have any ideas? This really is annoying because I purchased
this $600 card for gaming, but I always had the second monitor
configuration which I use in regular Windows desktop applications. In
the past, the second monitor just displays my desktop background while
I am gaming (or playing these demos), but if performance is this poor,
then I will have to disable the second monitor every time I want to
load a game, and that is silly.


- George