9006
9012:
Application notes This new Philips bulb is physically, electrically, optically, and legally compatible with all previous 9012 (HIR2) bulbs, so it can be used for all the same design-specification, replacement, and upgrade applications.
It can replace the 9006 (HB4) for special-service use; such a retrofit requires minor modification to the bulb base as described here Like all previous HIR2 bulbs,
it does not have a blacked-out tip, which means it should not be used in road going headlamp or fog lamp designs that don't have a bulb shield completely covering at least the top half of the front of the bulb — a ring-style bulb shield that leaves the front of the bulb exposed to the lens is usually not sufficient.
http://store.candlepower.com/ph3rdge90h.html
Goes back to the basic concept. A headlamp is designed for a specific bulb. When you alter the bulb, you will alter the light. they make a point of the black out tip. And I cant tell if the 9012 is a little longer, but by the link, it seems the only issue is the tip/