Finding out Speed of the PCIe Card

I have the assembled the following Rig recently:
E6750
Asus P5B Deluxe
Galaxy GeForce 7900GS superclocked(PCIe)
2GB transcend RAM.
Antec earthwatts ea 500W
Seagate 320GB SATA
Sony DVD Writer.

Now I get a beep code (1 long beep followed by 3 short ones) which indicate
a problem with graphics. The card works fine after the beep though. The card
gives this problem only when in the 16X slot and not when in 4X slot. Someone
suggested that the card/slot may have problem in running at 16X. I want to find
if the card is running at 4X or at 16X. Is there any way I can find it out? I tried
BIOS(American Megatrends) but found nothing. Please help me out if you know
about it.

Thanks in advance.