I hope I understood you well.
In few words, GSM v0.36 is more simple to use, by other hand v0.23x, allows more control about GS chip. You just must read carefully the first posts where GSM's FAQ is located, in order to realise how to make tweaks yourself.
In more words, If you want fractional adjustments for witdth and heigth in order make both vertical and horizontal black borders simply disappear, it's possible. But unhappily quite unprobable due to the needs of having these days some GSM volunteer skilled in TV color systems and PS2 development (reading GSM first posts about synchrization fields - vsync, hsync and so on), well equiped (at least with an oscilloscope) in order to deduct info empirically from experimentation of many GS vmodes settings, since we don't have all documentation we would like to have. So all this demands a couple of courage and spirit of sharing experiences, bring us his/her contribuition for implemmenting new relevant features on GSM. Or maybe someone could try to discover how some titles from Square Enix handle black borders (dlanor posted some stuff related about this suspection)...
doctorxyz's PS2 & PS3 stuff: (http://psx-scene.com/forums/f257/doctorxyzs-ps2-ps3-stuff-101348/)