I use 800x600 provided by Super72. By eliminating overscan I managed to improve the parameters to 27kHz/84Hz!!! The flickering is almost invisible... There`s other solution for CGX on AGA- CGX-AGA patch that can be found on AmiNet. I use it for years.. I have 040/40MHz and in companion with FBlit it works reaaaaly much faster than normally. Usng 256 color screen in not really comfortable for Workbench, but 128colors mode is several factors faster. I use 800x600, 128 colors for workbench and it`s really fast, because it is promoted to load images to fast ram, use simplegels and fastlayers. Few days ago i noticed that using Fusion wbwRefresh driver on my WB is t least 2 times faster than using any fullscreen driver! And all this on AGA... Using AWeb in this resoluton is comfortable, too.
If you want me to help you setup CGX-AGA in your system, please pmail me.