Schmanky: Put simply, framerate and drive performance aren't necessarily one and the same. Load times may differ if you use a better drive, but in general, fps is not affected, that is directly related to the work your cpu in conjunction with your gfx card can handle (at least when playing at low resolutions, at high resolutions, the gfx card takes over most of the processing).
I also have the Asus A7V, such as yourself, and while I'm unsure whether or not you would suffer from a performance hit using the pdc20265 promise ultra100 ide controller or not, I can honestly say that if such were the case, at least I haven't felt any decreased performance in my system.
I don't really know why they have the whole device (the controller, plus the drives) showing up as scsi, I just know they do, and that's fine with me, as long as it works, heck - maybe it gives you better performance, who knows?
The only hassle with it are during installs such as win2k where you have to have a floppy ready with all the drivers during the first install phase (and you have about 1-2 seconds to press down a button to let it install a scsi interface), but that's basically it. If you're getting bad results, it could be because of the drivers for that specific chip, I use the latest I could find (which are 1.60 build 33). When A7V was still active
, ie. being sold, there was talk that burst performance of the versions that came bundled with the motherboards were poor, and pretty soon thereafter another version came out. At least it wouldn't hurt to try if you haven't already!
Hope that clears a few things up.
PS. I would conduct benchmarking on my seagate, but it's a 2-platter version (60gb) and would therefore not be representative for your little 'investigation'.