Instead of Westone W3 with just 3 Balance Armature, try Westone W4, with 4 BA, that should be a fair comparison with UE900 which is also 4 BA.
as for my personal listening IEM, I'm inclined towards Westone W4, but that just me who doesn't like bright and sparkly Treble.
Interesting. I have a Westone ES5 (actually, only the left one because I am partially deaf, so the cable is wired by Westone to put both channels into a single IEM), and the one criticism I have with it is that the treble is too smooth/inoffensive. Bass and mids are incredible, and certainly the treble has great clarity, but it likes the "sizzle" or sparkle that I love. That's actually why I'm leaning towards to the UE900. I can at least listen to it and then decide whether the SQ matches what I'm looking for (and return it if it doesn't); with a custom IEM, you gets what you gets.