Yes all of you can use a Sparkle bios.Or Asus one,or MSI.
Moded bioses for voltage just don't work for me.They don't change voltage for real.
For Leadtek,you will see an improvement in core overclocking.
For Palit.I don't know since there is no molex conector.Same problem like Inno.AGP is limited to max 40w power supply to the card and rising AGP voltage in bios does not help overclocking,but it is ment for something else,concerning Northbridge_AGP link.It might help stability,though.
I currently run my Sparkle at 600/780 with changed timmings.