Hi Dr.Venom,
I have spent a good amount of hours these days trying to get something useful out of my HD 6450 & Cat 12.4, and finally I've given up. I thought there was possibly some hidden registry key that might redirect these cards into the path of virtue but all efforts were futile. The fact that these cards work perfectly under Linux means that it's just a software matter, so it's virtually possible to fix this situation by a clever hack of the Windows drivers, but reversing the Catalyst monster to this extent is definitely beyond my capacities.
Basically the new AMD cards won't work with arcade monitors because when they don't "feel" the monitor they enter a sort of dumb mode as soon as the drivers are loaded. So you can see the boot fine but once in Windows you're stuck with a 4-bit colors mode. No matter what you try you can't change the video mode.
On the other hand, if you plug a CRT with a valid EDID, the card works fine, but our custom modelines are completely overridden by some uncertain refactored modes that have nothing to do with the user defined timings. The modelines are certainly read and checked, because the refresh rates are taken into account, but they're rounded and recalculated to meet the monitor's capabilities, so a 15kHz mode will become 31 kHz. The worst part is that many resolutions, especially the low ones, are hardware stretched!!!, no pixel-perfect any more. A colossal load of ---steaming pile of meadow muffin---.
After booting with a PC CRT I can switch the cable to my arcade monitor (tri-sync) and so the dumb mode is avoided and I can switch resolutions on the arcade monitor. Anyway no 15 kHz is possible as the driver is still contaminated by the previous EDID information.
I believe it's not only the lack of EDID what makes these cards enter dumb mode, it has more to do with not detecting the arcade monitor (no 75 ohm load):
http://soerennielsen.dk/mod/VGAdummy/index_en.phpAnyway, this was just to confirm that unless a miracle happens, under Windows, we're going to be stuck with the HD 4000 series for CRT support. So I'll try to focus on providing modded driver support for these cards on W7. I'm not sure yet if it will work at all. For economy, I'm just going to work with 64-bit drivers. I'll probably try with two versions, 13.1 and 9.3. The 9.3 is just to check if dynamic modelines ever worked under Windows 7. If I had to choose between dynamic modelines support vs want latest version my answer is obvious, but at least the user will have the possibility to choose.