Aside from synthetic benchmarks, I sincerely doubt you'll see any difference between DDR4 3200 and DDR4 3600. Go for 32gb - and make sure to grab a 2 x 16gb dual channel kit, not a 4 x 8gb. I've heard (haven't experienced it myself, only rocking 2 dimms right now) that overclocking kaby lake is tougher with 4 dimms populated.
I've got a very similar setup for my gaiming rig — Maximus Hero IX, i7 7700k, 1080 strix, 32gb DDR4 3200.