Just stumbled upon this thread, although I did post a response in another thread to this very same question. Right now I'm running an Areca 1230ML in the second PCIe X16 slot on my ASUS P5E3 Deluxe WiFI AP@n without any problems. However, originally I tried placing the 1230 in the X4 PCIe slot and this configuration did give me boot up problems for some reason that I have not been able to pin down. I did buy a 3Ware 9650SE controller and was able to run that card just fine in the X4 PCIe slot wihout any issues at all, but the performance is just not the same as the Areca 1230. So after much frustration and wasted time, I finally decided to try the 1230 in the second PCIe X16 slot and was very happy to find that it works there just fine. Hope this helps some of you make a decision.