The GX is the original cg6, with the TurboGX version being basically the same hardware, just a bit faster. The both have one mibibyte of memory, and supports resolutions of up to 1152x900. Refresh rate depends on the actual version of the hardware, with 66 hz being almost always available and 76 hz being available on newer release.
The + version of the framebuffer have 4 mibibytes, and supports resolution of up to 1280x1024 (GX+) or 1600x1280 (TGX+) and double-buffering.
The SPARCstation LX on-board framebuffer is a regular GX, but with a slot to expand memory to 2 mibibytes, allowing resolution of up to 1600x1280.
Note that it is impossible to have more than 256 colors (8 bits depth) on any GX with any amount of memory.