I've considered that motherboard too, and the information I got was that they are backwards compaptible and so allow the use of Raptors and any other 1.5gb hard drive. You could ask ASUS themselves, or Newegg for that matter, as they would probably knwo, since they have to warrenty the things.
There isn't a drive or an array out there that can saturate the SATA bus...let alone the SATAII bus. So, even if the Raptor did work at the full 300Mb/s transfer rate, instead of the 150Mb/s standard it will use, you wouldn't be able to saturate the bus.
Googling is fantastic for answering fairly simple questions, but I had a rough time figuring this very question out a couple of weeks ago. Give the guy a break. It's not obvious, and google can be uncooperative if you don't know exactly what you're asking.
Soon after SATA's introduction, enhancements were made to the standard. A 3 Gb/s signalling rate was added to the PHY layer, offering up to twice the data throughput. To ensure seamless backward compatibility between older SATA and the newer faster SATA 3.0 Gb/s devices, the latter devices are required to support the original 1.5 Gb/s rate.
Third paragraph in the second googled entry for "SATA".