3 monitors gaming

Hello to all,

I got:
630W
M.BOARD ASUS S775 P5K + gigalan Intel P35
INTEL Q6600 CORE 2 QUAD 3.00Ghz 8Mb DI CACHE - FSB 1066Mhz
RAM 2Gb DDR2 833Mhz in dual channel
VGA Nvidia Ge Force 8800GTX
3 monitors samsung 21" 214T and matrox tripplehead2go digital edition ang I get max resolution 3840x1024...  (
I play with flight simulator 2004 and I get 5/6 frame rates (full desktop) instead of 20/25 I used to have without Matrox and with 2 monitors (resolution 1600x1200 at each monitor but not on a full desktop) ...
Why can't I get resolution 5760x1080?Or why can't I keep the resolution at 1600x1200 on each monitor (4800*1200 in total)?
Should I change cpu, mother board, VGA?If yes wich will do my case?

Please help