Hi there
In my current version of coreboot I use OptionsRom as VGA BIOS. But earlier versions I used VGA-BIOS out of original BIOS by command or by perl script.
A diff on command generated VGA BIOS and OptionsRom shows many differences. But I don't know where you got OptionsRom.
A diff on last two shows that perl script generated VGA BIOS is only smaller. Data inside is same as in BIOS got by dd command (see http://www.coreboot.org/VGA_support).
Next step I will try to use my own generated VGA BIOS to look if this will run, too. If you are interessed in original VGA BIOS, let me know. I don't want to send it to mailling list.
Greetings Klaus