How seriously do dual monitors impact gaming fps?

[Tripl]

Like many OP's, i excuse me now for not being able to search if a similiar topic has been posted before.

My question is in the title: "How seriously do dual monitors impact gaming fps?"

I'm asking this question because i'm thinking that my current system is a bit underperforming.
System:


Clarification:
the HDD partitions are from one and the same RAID0 setup with 2 1TB samsungs
the Graphicscard is a HD4890 OC with 1gB of ram

Monitor setup (as you can see from the pic) 17inch CRT on 1280x1024 (connected trough DVI>VGA) + 42inch LG HDtv on 1920x1080 (Connected trough DVI > HDMI)

Now why i ask is: I usually do dailies, farm runs, pvp etc on my CRT and like to raid (and play epic games like AC2) on my TV, and i noticed that on both screens my FPS is suspiciously low, for wow between 20 and 50 FPS (Ultra ofc, not going any lower with such specs)
the other screen is usually just Idleing, during raids my CRT is on wow wiki for strats etc, when i play on my CRT my tv is usually just playing a TV (aka showing content from the cable, not the pc)


TL;DR: Low FPS with a (in my eyes) monster PC, can dual monitors cause this or should i be looking somewhere else?

[vesseblah]

Radeon 4800 series graphics card is your problem. I have Radeon 4850 myself, and FPS in raids is about 20-25 on FullHD resolution with all graphics to max. When I turn shadows off, FPS increases to 50-60.

Having 2 monitors plugged into PC will not make any difference as long as WoW is running only on one. But there is going to be huge difference in FPS between 1280x1024 and 1920x1080 screen sizes. Bigger screen has almost double the amount of pixels to draw.

[lethalnl]

if its 2x the same image there is little difference, if it has to strech or split the image it will make a large difference in framerates

[H3ll]

i have roughly the same specs as you (the only difference is the mobo and hdd) and im using a 1920x1080 and a 1680x1050 screen. I can run most games with 60+ fps on my 1920x1080 screen in fullscreen, or windowed @ full screen size. While playing wow @ ultra my fps was also pretty low (20-30 in 25mans), esp compared to games with way better graphics. I tried a lot of things, but the only thing that seemed to work was putting shadows lower, after that my fps increased to 60, even in 25 man raids