i think they're closer in brightness and efficency than we give the rebel credit for.
That's my understanding also.
For a while the Rebel seemed to be king, now the Q5 is contending with it. I don't think there's a clear "winner" at this point, though.
Mostly personal preference between these two as far as emitter only goes.
Actual performance in a light is going to depend on a number of things, and you can easily have a light with either emitter from a certain manufacturer being more efficient and brighter than a light with the other emitter from another manufacturer.
The Rebel might be just a leetle more efficient.
I personally MUCH prefer the tint of the rebel to any Cree I've seen (though I have no experience with a Q5) - not so much because of the actual "tint" of the light, but because of the superior color rendering from the Rebel. It brings out reds and warm colors much better than my previous Cree experiences.