Interesting development regarding OEM ICR headset creaking. At some point I started noticing the gap between headset top cap and the bearing cup underneath it is skewed, ie. wider at back than at front. After putting some thoughts into this I came to the conclusion this is probably caused by the stem with split clamp flexing under the force of preload screw, which needs to be tighten unusually strong on this headset to remove play. At this point I was using stem like in the pic below.
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After trying out stem with solid clamp like below, the gap is now even and the creaking is gone. I haven't had a chance to put this under heavy stress yet, but it seems resonable to assume that skewed top cap was putting uneven force on the split cone and the bearing underneath, resulting in creaking noises when turning handlebar left/right due to cone and bearing seating.
View attachment 141155
The stem I tested it with is a temporary solution, I ordered green Deity Copperhead which also uses solid clamp. I guess the problem isn't really related to the stem material (softness of it), the same stem would work fine if the headset didn't require so much preload force. Anyway, solid clamp seems to fix it.