RandyP, thanks a lot for your pirep. Hopefully this thread will get more pireps as more pilots try the PFX.
I just called Lightspeed to try to get an answer to my own question and found out a couple of things people here might be interested in. First, as of yesterday they've included the PFX in their trade up program (their website has the details). I know some people have been saying they'll hold off on considering the PFX until Lightspeed includes it in their trade up program.
Second, the Lightspeed rep did confirm, as Bcm25 posted, that there are two ANR settings on the PFX and the first level provides ANR that is "very comparable" to that provided by the Zulu 2. (I take that to mean basically the same.) That is a fixed noise cancelling that is "hardwired" into the headset at the factory and does not change, she said. However, when you switch to the second level, the headset samples the surrounding noise through microphones on the ear cups and then adjusts the ANR in response to the specific type of noise it detects occurring in your environment, giving you a "customized" ANR that's supposed to be better than the base level.
I asked about Bcm25's statement that you had to stay in the first level of ANR if you are in "loud open cockpits (cub)," and she asked me if I fly an open cockpit aircraft. I said, "no, but I fly in a noisy aircraft," and she said that would not be an issue for me and that the PFX would provide the best noise protection I could buy for a noisy aircraft (obviously the last part is a salesmanship statement I'm not able to confirm, but I'm just repeating the conversation). The headset has microphones on the exterior of the ear cups that sample the ambient noise and if you are flying an open cockpit aircraft where the wind stream really rushes over the microphones, you may have to stick to the first level of ANR. But she said that is not the case in all open cockpit aircraft, just in some; it depends on just how much wind is rushing over the microphones.
Anyway, that's the info I received. I'm not a Lightspeed rep and don't own a PFX - just someone with the Lightspeed 3G series who is considering trading up.