Yes the Hyperion 4in1 version 4.55vp1 is "smart" and it does detect that you are running SP2 so consequently, the VIA AGP3.0 Support portion does not show up during the install so that your AGP Support will default to the M$S AGP UGART3.5 standard....
Although the VIA VT8237 is indeed a part of the "SouthBridge" that also is where the IDE Channels are connected to....I do not agree with your conclusion that:
"XP/SP2 does not recognise the SATA features of the VT8237 chip and so creates another set of IDE
ATA/ATAPI controllers, but cannot cope with both so allocates the same parameters for the second set as the first. Therefore the performance of SATA depends on the IDE devices or if no IDE device
present defaults to PIO."
Take a look at what I SEE in my Device Manager:
Are you SEE-ing essentially the same controller settings ?
If you are running a RAID-0 it does seem slighly slow on the controller for you ...Take a look at this thread
and I am curious about the RAID Tool "pop-up" that quickly dissappeared ?