SAS/RAID Adaptec on Rampage 2 Extreme?

hello,

a little hardware question

i have a Asus Rampage 2 Extreme motherboard which contains 3 pci-e slots 16x-16x-??x

i have 2 pci-e slots used by 2 gtx280 graphic cards in SLI

is it possible to have in the third pci-e slot an adaptec 5405 8x to do raid 5 with 3 ou 4 hard disks

in that way, what is the speed of this third pci-e slot ? 8x, 4x, less?

and also i would like to know if my 2 graphic cards stay in 16x or if the speed of the second card fall down to 8x?

im weird because i see that specification:

"3 x PCIe2.0 x 16 slot, supports x 16, x8, x8, or dual x 16 speeds"

at last, what the impact on the performances?

thanks

Last question first:
I don't think you will see any performance improvement in gaming with raid-5 or with 15k sas drives.
The velociraptor or using only 10% of a wd caviar black 1tb drive is about as good as you can do with conventional drives.
If you have the funds for a good raid controller and sas drives, then I suggest two intel x25-m ssd's in raid-0.

First question X16,x8,x8 should be fine. The GTX280 can hardly saturate the bus.

i will buy the 5805 Adaptec first then test it and maybe swap velociraptor hard disks to intel x25-m ssd after