Well, I got my board last night along with a Promise ATA-100 controller. I took my old crash-a-minute KT7-RAID out, swapped it for my new board, stuck all the cards in (modem, GTS2, ATA-100, sound), plugged everything else in and turned it on... And it all worked! It managed to boot into Windows without any problems using my set up from my old KT7-RAID. It attempted to find drivers for the Promise card and various other things, so I installed the Promise one and disabled the rest from the BIOS. And then I updated the BIOS to the 2000/11/03 version (1.8?), reformatted everything and reinstalled Windows from scratch. The board took everything I threw at it without any problems at all - I am even using ACPI which I wasn't before as it hated my Abit board. The only thing I need to do now is reinstall Linux.
One little problem: my internal modem causes a system hang-up when it's dialling (it's a US Robotics V90). However, my external modem works a treat... I fired up Sandra and the modem is sharing IRQ5 with the USB controller, which I'll try disabling and attempt to dial up again, after reinstalling the modem drivers.
Performance? Can't say I notice much difference, really. All the figures in the comparative reviews I've read (incl. Anand's) have fairly similar results.
To conclude: buy this board now! (Or the 'A' version). It kicks ass. If this carries on like this, MSI have got themselves a life-long customer... [unless my PS2 which I get on Friday is better...]