I'm quite troubled about the low isolating value you seem to attribute to the Sennheiser though, as I would buy I mainly for use on public transportation.
I e.g. use the Yuin G2 at work or when I'm on the move and don't want/need isolation. I just love it's sound (eventhough it lacks in the lower frequencies/bass), but it's just not up to the isolation-task when used on trains or airplanes. I have the Sony MDR7056 which is better for that, but still, I hoped to find in the Sennheiser better isolation in a more compact form...
I don't really mind hearing the (attenuated) casual high pitches of a train's breaks when entering a station or noticing that the train conductor is announcing something, but I'm mainly looking at eliminating the constant train-noises (motor, wind-noise when the windows are open, rithmic sound on the train-tracks, most of the background noise of the people...)
Hi blub, maybe I was being a bit too critical of the passive noise isolation plus noise cancellation. I'm so used to totally blocking out the external noise when working out at the gym (very loud music) with Shure or Klipsch IEMs (music at volume level of 6 or 7).
IEMs 9.5/10 for noise isolation gym, train, buses etc.
With the PXC 310 BT I have the volume level on max and I can still hear the gym music but not to the point where it takes away from my music experience. With the noise cancellation on it blocks out the bass part of gym music (but I'd rather not trade off my listen experience to turn the noise cancellation on (maybe I'm not used to noise cancellation but it feels a bit eery or unnatural).
Noise isolation/cancellation at the gym: 7/10
On the subway, I think the supra-aural closed back design coupled with noise cancellation does an adequate job of blocking out external noise of the subway (motor, humming engine etc.). Plus the the music you're listening to doesn't leak too much sound to the point where others around you feel uncomfortable. And buses are fine as well as they're less nosier than trains.
Noise isolation/cancellation on the train: 8/10