If you love your W4R then I'd recommend you stick with it. All of the $400 (to 500 range) IEMs (that I've tried) are on par with one another (with slight differences that appeal to personal preference rather than better or worse).
I compared a W4 and 535 side-by-side for a month. I can say that what the 535 offers is a more emoting mid center vocalist. I could not EQ the mid-vocalist range using software players (on Apple, Android, Sansa, or Cowon) to level the field with the W4, SM64, UE900 and others. I think It would take a more comprehensive EQ to achieve the mid vocal range emphasis of the 535 on other IEMs (that I've tried). But this 535 advantage is a slight thing that was more important to me because I had the 535 first (and for a long time). I am very accustom to its sound. On other IEMs lead vocalist tend to sound flat (and uninspired) even on otherwise superior (and more expensive) IEMs.
BTW, turning up the bass and treble to level the 535 with other IEMs is easy and it works well. I can't get it to do what the IE8 or 846 can do but its good for most songs (in my collection).