Well, I'm currently deciding wether to buy the 16-55 or a couple of primes (35, 16?). I want fast AF for the occasional action shoot and and shallow depth of field/light gathering capabilites. The 35 f/2 sounds like it will offer better AF speed, BUT it would also only be F/2 - which is very close to 2.8 from the zoom, so the advantage is kind of negated for me.
Btw, I'm a flexible shooter. I enjoy shooting primes but also the flexibility of zooms. Just in case you're wondering.
one important thing , you didn't mention, to consider is the size and weight. The f2.8 zoom lenses are huge compared to the primes. The 35mm f2 WR is going to be even smaller then the classic 35mm f1.4.
If its only about light gathering f2 is still a full stop faster then f2.8. If it's about dof the 35mm f1.4 stopped down to f2 will still give you nice bokeh. Don't underestimate an f2 lens. It's plenty fast and still has nice thin dof. Remember that the x100 series is "only" f2.
Personally I don't think the 16-55mm f2.8 isn't worth it because:
- no ois
- no internal zoom
- large and heavy
- get the cheaper and smaller 18-55 with ois http://admiringlight...18-55mm-f2-8-4/
And if you want fast and thin dof get the 56mm f1.2 instead.