Holy crap... Just got my "X600", which turned out to be something that doesn't exist
The BIOS says its an RV380XT, which would be some kind of X550, but it ALSO says (per device ID) its an X600 series
Another funny fact is that it has a 350 MHz core clock and a RAM clock of 250 MHz (500 MHz DDR) which also doesn't match any of those ATI reference cards
The best part is the catalyst driver which say its an "ATI Radeon x300/x550/x600/x1050 series"...
Whatever...
This card can go down to about 4MHz pixelclock which is fine for 240x240 (and lower) resolutions, however it does not show 321x240, 321x256 and 401x256 pixel resolutions in the list... Also it shows 320x240, 400x300, 1024x480 (and various others) resolutions which will be output in 31+ kHz.
As for now I can't get them "removed" from the list.
Well... Lets see what the weekend offers