Dual Monitor Performance

My current system:

C2D Q6600 @ 3.6GHz
4GB Mushkin HP2-6400 RAM (800MHz)
8800 GTS 512MB (G92) Vid Card
x-Fi fatality Sound Card
24" Acer 1920x1200
Vista Ultimate 64-Bit

The actual post:

My current monitor is acting up (again, but not like it has before). When it gets turned on for the first time in a few hours the display is all messed up, just random vertical or horizontal lines that move around. After a minute or so it goes back to normal and works fine. So I decide to look into another monitor. I'm debating getting a BenQ 241W 24" and have dual monitors. Thus if my current monitor goes bad I'll still have one. Or I may get 2x 22" monitors and keep dual monitors (the price would be about the same, 2x 22" or 1x 24"). Basically I would go from 1920x1200 to 1680x1050 resolution.

I'm also interested in starting to two box (WoW) - I've done before, just alt tabbing between the windows (only one is shown at a time). But I'd much rather have 1 version of the game on each monitor. Once I figure out my monitor issue I'll continue to research the software and what not to get it going.

Basically I want to know if there will be a noticeable performance hit running 2x 1920x1200 games versus 2x 1680x1050 games, using just the one video card.