If any of you have run the LED reverse lights from Retro-Solutions, you'll have a pretty good idea of the difference before and after. Significantly brighter than the stock headlights with halogen bulbs (at least 9007 bulbs). Light projects further down the road, better peripheral illumination and still a relatively crisp cutoff so you aren't blinding oncoming traffic.
I would still take a properly aimed projector with HID over the LED's, but they beat the hell out of HID's in a stock housing.
I'd rate them: HID's w/ projectors > LED's > Halogen > HID w/o projectors.
Keep in mind I don't own a 6.7 so I don't have any direct experience in that regard. I have run them in my OBS, Mustang, Jeep SxS and ATV with positive results in all of them.
The light output in terms of color and clarity is comparable to LED light bars.