m209- the v2.0 isn't all that different from the 2.5- the 2.5 just has a smoother textured reflector and has a bit more power going to the LED (more light, less runtime). I've got the 2.0 and have a 2.5 on the way. I also have a QIII.
While the stats of the L1P vs QIII look different on paper, I think its easy to compare the two lights and find that in pretty much every way, the Fenix comes out on top. For one, even though the QIII uses a smaller (well, shorter anyway) battery, the Fenix still manages to be a tad shorter than the QIII, and is much thinner. This is due to the deep QIII reflector, so note that the QIII has a narrower beam than the Fenix.
The HA finish on the Fenix is a matte black. While it might not be as durable as the glossy HA Nat finish as seen on the Jil Lites, it does a pretty good job; I already dropped the light on the pavement by accident and it only got a few small dents and only one tiny dot on the bezel where the finish actually came off. If the same was done to a QIII, the shiny aluminum would be visable all over the place.
The QIII switch juts out slighty from the switch guard so it cannot stand in candlemode without modding; the Fenix stands on its end without a problem. Both switches are reverse clicky, but I have read that recently the QIII comes with a sort of "fake" momentary on in its reverse clicky switch.
The output of both lights is comparable to my eyes- both are nice and white, but this often has to do with the lottery. In terms of runtime, the stock QIII will run for about an hour on its CR123 and has a habit of suddenly plunging into darkness. The Fenix runs for 2 hours to 50% on a standard AA alkaline or over 3 hours to 75% on an e2 lithium, and doesn't just crap out all of a sudden; you will still get several more hours of useable light (note that these stats are for the v2.0, the 2.5 will have a little bit shorter runtime).
The QIII is a perfectly good and reliable light, but I just sort of feel like it's had it's day and the Fenix outclasses it. Keep in mind, the Fenix L1P also comes with a special optical glass lense, a replacement switch cover, replacement O-rings and a nice warranty; its intended to really be used as an EDC (and has been performing perfectly over the past few weeks that I have been EDCing it).