To maximize the speed of the Mach64 X server, I suggest that you use the following maximum resolutions. This will allow room for the font and pixmap caches and a hardware cursor.
Max Resolution BPP Video RAM
-------------- --- ---------
1600x1200 8 8Mb
1600x1200 16 8Mb
1280x1024 32 8Mb
1280x1024 8 4Mb
1280x1024 16 4Mb
1024x767 32 4Mb
1280x1024 8 2Mb
1024x767 16 2Mb
800x600[*] 32 2Mb
1024x767 8 1Mb
800x600[*] 16 1Mb
[*] - With a 2MB video card, the only way to use the font and pixmap caches is to have a virtual resolution of 1024x480 with a 640x480 mode. I suggest using 800x600 to maximize your screen size at the cost of the speed gained from the caches. The same argument can be made for 1MB video cards running in 16bpp mode. Note that it is not possible to run in 32bpp mode with 1MB of video memory.
Technical explanation for the above suggestions: The Mach64 X server uses a font and pixmap cache that is only available at a screen width of 1024 or greater. This restriction will be removed in a future version of the X server. To obtain the best performance from your video card, you need to make sure that there is enough room off-screen for the caches (at least 1024x256). In addition to the cache, the Mach64 uses memory mapped registers which are mapped to the last 1024 bytes of the memory aperture. This takes away another line from video memory. Thus, you need at least a video memory area of 1024x257.