Talking about isolation.
My experience with Sony EX51LP is not up to my expectation. While some on other forums ie headfi.org said that it provides an OK isolation, others said the isolation from this Sony is not good. My take is it depends on how you use it.
1. If you use it in a relatively low noise area

office, airplane, library, Sony EX51LP should be able to block most of outside noise enough so that you felt rather quiet.
2. If you use it in really noisy environment,

on the bus without aircon and in the subway, the isolation Sony EX51LP provide is not enough and, to me, does not mean much.
As such, I bought the EX series but never used it on subway but more likely in the library, office to block out some noise.
There is some difference between Sony EX51 and EX71, I believe it's mostly on the body of the headphone. EX51's body is made of plastic while EX71 is from a rubber

material

its top of the line E888. So EX71 should be more comfortable to wear. However, I end up with EX51LP because I don't

its short cord version of EX71SL (or SP). The "S" at the end means that the cord length is only 0.5 meters which fit well with portable listening as long cable tends to tangle up. However, when you use it for normal listening and you're stationary, you are likely to use the extension cord, another 1m cord that comes in the package with EX71SL.
The problem with extension cord is that the canal type headphone

EX series has a microphonic effect. When the cord of your headphone was pull or touch, you will hear that touch amplified (microphonic) so loud into your ear and rather annoying. This is less likely to happen ever on earbud.
The extension cord will make the matter worse as the connection jack is rather heavy vs the cord itself. The added weight from the jack will make the microphonic effect ever worse. Plus, I doubt whether there is any degradation of sound quality due to connection jack. My experience is that the sound is softer with much less detail if you use the connection cord.
On top of that, I don't

its tonal balance and its sound and probably will not use it for a long haul,

international flight. I would rather use airline headphone to watch movie than this Sony EX.
Just my thought/experience on canal type earphone. It's rather confusing to read all those review on the net and all of them tends to be different from others without any explanation.
Pls feel free to jump in and point out whether my thinking is right or wrong in any way.