Since my monitor doesn't support the PS2's interlaced RGB, I always have the console set to YPbPr, which it does display in green, so I can navigate the menus to GSM.
I will definitely try GSM in RGB mode today and see what happens.
If I had a decent TV I probably would use component only. But right now my monitor is pretty much my only choice for decent progressive scan. So in terms of GSM, a working VGA mode is really the only thing that matters to me...