Ah, well, they're the same size. Like exactly the same. The W3s have a large driver for bass (No idea which ones), the W4s have two smaller drivers instead. The nozzles are just as short, but there isn't any sibilance unlike the W3s, so extremely tight seals with long tips aren't necessary. In that sense, they can be even more comfortable.
Sound-wise, they are much more balanced and inoffensive. The bass hump is still there, but it has gone down drastically. Treble is now laid back, and the mids are more forward. Completely beats out the W3s in technical proficiency. Soundstage isn't as diffuse, the presentation is much more natural. While clarity is still better than the W3 by miles, the slight midbass hump can give a slight veil to the lower mids. This can be somewhat remedied through EQ and tip rolling.