I don't have a solution to your problem. I wish only to add that I experienced something similar with my MX440, so it's another data point to consider.
When I tried to configure X during the RH 8.0 install process, none of the 24-bit modes would work at any resolution (this was using the vesa driver that the installer chose). I haven't tried setting the depth to 24 since I installed the NVidia driver's though.
I also rebuilt the srpm's, so it will be interesting to see if I have the same problem you did. I'll try it in the next day or so.