Asus P5Q Pro & Adaptec 5805 Raid Controller

Hello,

I have a Asus P5Q Pro Mainboard and want to extend my system with a Adaptec 5805 RAID Controller. My board has 2 PCIe x16 slots and the RAID controller will need a PCIe x8 slot. My graphic card is a Sapphire X1950Pro which is in one of the 2 x16 slots. I know, that the board will slow down the both x16 slots to 8 lanes in CrossFire mode. I've no problem when the relativly weak X1950 runs only with 8 lanes. The question is: will the RAID Controller work in the 2nd x16 slot (with 8 lanes) or are both slots for graphic cards only?
This diagram of the P45 says, that both are for graphics. I'm really unsure because i thought, PCIe is for every device.

Please help because i don't want to buy this expensive RAID controller and can't use it.
Thanks in advance!

Best regards

Thanks for your answer. I've found this post but wasn't sure if this applies to the P5Q Pro too because the board in the other thread is a X48 chipset and the P5Q Pro has an P45. I just want to clarify all things before i purchase the controller.
Has anyone such a combination?