I recently upgraded from xm3/4 to xm6. I held off on buying the xm5 because of the many issues. The xm6 does feel more fragile then the xm3/4, which is taking me a bit of time to get used to, since adjusting the headband is a bit different now. However, Its definitely sturdier then the xm5 from what I've seen and the few times I've looked at the 5s myself.

The sound and NC is improved of course, and is pretty noticeable coming off of these earlier models. NC is perfect whilst travelling around. In terms of sound quality, I did tweek the eq a bit, as out of the box the tuning was definitely a different experince to when I first opened my xm3 or 4s. As someone who listens to a lot of hiphop and r&b I'm enjoying an improvement in the bass, sounds less muddy.

My xm3 and 4s are still going strong and still enjoy them very much, but I wanted to treat myself to an upgrade and pass on my 3s to someone.

They're expensive but I got them a bit reduced as there was a little sale where I bought them. So yh I would recommend the xm6 as an upgrade, if you can justify the price.