From what I've read the yamahas tend to be a bit finnicky in fit. As I use them at work I need to keep it fairly simple! With regards to the westone 3 recommmendation I did indeed have one and enjoyed it immensely. Right up until the point they went in the wash! Sadly it did nothing for the treble but the bass went on them, hence why I picked the x10 as a cheapish replacement (amazon offer+voucher anyway). Nice to see I was on the right track (backwards!).
Did you keep your W3s? If you did, I would recommend sending them in to be recabled by Westone. I had my UM3Xs sent through the wash a couple times due to my carelessness and my wife's unwillingness to care about my carelessness . As you said, the treble was fine, but the bass would rattle above anything more than a whisper. I emailed Westone, and they said to send them in. They took a look at them and recabled them for 40 bucks, and they are perfect again. I am also very glad because they gave me a newer, smaller plug that is much easier to deal with than the original I had. I would say it is at least worth looking into for such a nice and costly IEM.