I have a question, I'm a bit confused about the PCI-E 16x slots on this motherboard.

So it says the first one is 16x which is what my 9800GTX is in, and the manual says the second one is 8x and when you do crossfire it is 8x/8x.

If I buy a raid controller which is 8x, will it run at 16x/8x or will it drop to 8x/8x since, if so is there a way to force maybe 16x/4x?