X2 Motherboard and PCI-E 16x video support

It occurred to me that paulwhooppee.com wrote in
gmane.os.netbsd.ports.x86-64:
> And what PCI-E 16x video cards are known to be working?
> Especially with X?

I'm running an Ati radeon x300 (Cheapest PCI-e video card I
could find at
the time ... ):

vga0 at pci5 dev 0 function 0: ATI Technologies Radeon X300
(RV370) 5B60 (rev. 0x00)
wsdisplay0 at vga0 kbdmux 1: console (80x25, vt100
emulation)

on an Asus A8N-E, using a 3000+ (No X2). Card seems to work
OK with xorg, and
can be made to work with XFree86 too - but this involves
overriding the chip
ID, making X think it's actually an RV360, aka radeon 9600.
For plain jane
2D this seems to be valid.