Thanks a lot Bikemig !!
I browse amazon, and can tell that the AKG 550 / 551 and the Sennheiser PXC 450, were on display at the Good Guys / Magnolia Hi-Fi in Burbank, but unfortunately not hooked up (they said the connecting cable broke). I am going to call the store manager and ask if they can repair it soon so that I can go and audition them. I did noticed that the AKG were built well and sturdy, seemed like a metal / aluminum frame.
The noise canceling may be important during flights (example Australia 15-hours), but, I usually stay in the hotel for couple of weeks at a time, so yes, there is a trade off there. Wouldn't want to compromise the audio quality too much. Also, I love classical music, jazz, instrumental, vocal, pop, and Rock, so here again it is difficult to have all the best performance in one headset. I created a music sample of 10 songs on my iPhone of my favorite pieces so I can test all the headphones against the same music.
When I visited Magnolia Hi Fi, the PSB M4U 2, and B&W headphones bank was the only one that worked. I must admit, that the PSB's and the P5 were better than the P7 to my ears. The nice thing about the PSB was the built in amplifier that when in use switches the headphones from 32-ohms to 10k-ohms, which reduces the power consumption of the source iDevice, and it gave it an added "punch" which was nice at the bass response, but more importantly, it changes the frequency response of the headphones, such that it sounded "fresh" if one got bored with one frequency response function. also it had a built in noise canceling function, but I couldn't determine how effective it really is ? Then I was impressed with the B&W P5 way more than the P 7 ! They sounded overall more balanced frequency response and seemed to isolate the noise well enough such that perhaps it didn't need the noise cancellation ? The one major plus is that they are half the weight of the PSB !
Oops, almost forgot, but I was also able to listen to the Bose QC15, yes they were good sounding too in the store. But overall, I would say that the PSP and P5 delivered a more "exciting" presentation. I only have experience with Bose exercise headphones which broke very quickly, after few months, and I replaced that with Sennheiser Addidas, which I have been using ever since for few years now with no failure or degradation of the sound quality, albeit, not audiophile quality.
I will report again once I am able to audition the Sen PXC 450 and the AKG's you mentioned.