My main PC is like your new one.. almost exactly but i run two 280GTXs 2x 24 samsungs. I run all 5 ( not symlinked ) and run through Dalaran with zero lag. ( I always have alts on low setting though, and main on very high settings ) I still have an issue when i use PiP to swap screens. I freeze up and have to alt-tab out and back in to fix it. Other than it runs like a champ.

I play FPSs as well. Far Cry2.. Crysis ( both ) Fallout3 and i have all setting maxed on all of them with very smooth FPS ( from 50-100+ depending on the game ) Unless this one blows up, I'm set for awhile 8)

my PCs specs are
i7 920
12G Tri Chan DDR3
2 280GTX ( SLI )
Patriot 128gb ata SSD drive
Vista 64 Ultimate

Because of the PiP problem I am thinking about going with the 2 PCs so i do not have to swap screens ( 5 PCs is too much for heat/space for me )