I've not tested the P2D Q5 but here's my best informed guess.
I prefer the Rebel 100 that I have for these reasons:
1. I prefer the tint of the Rebel.
2. Rebel has lower Vf and hence, should offer two significant advantages: On a L1D body with one AA, I'm almost sure that the Rebel 100 will be noticeably brighter. It will also offer longer battery life being more efficient in total watts consumed.
HOWEVER, if you are running on turbo for extended periods all the time, the Q5 has better heatsinking ability and should be more durable. The difference may be moot though given that the Rebel does just fine.
So, for me, it's the Rebel 100. Anyone want to get rid of your Rebel 100 for cheap now that the Q5 is out....
? Gimme a holler via PM.
Moses