Regarding frame rate, all of the G5 drawing is done on a separate thread, then the pixels are copied over during the gauge drawing callback. The library we use for drawing has an update in testing that would allow for asynchronous uploading of these textures to the GPU which should help a bunch with performance, idealy reducing the G5 to near zero for non-thread-limited CPUs.
Regarding the dimming function, that is currently not implemented, but it is a highly requested feature so we have it on the list!