At least they do at level 12 fighting level 12 mobs.
I'm a 10 FvS / 2 Mnk. It takes me longer to kill gnolls with these vorpals than with my zero crafting holy burst scimitars.
I'm not complaining, and I suspect that as I level that I will find vorpals to be better as I'm told mob health increases dramatically. I just thought that I'd share my experience in case others out there are wondering whether to try to get vorpals at <= 12.
Regards,
Teran