Thanks to the folks at Faster, I got a few insights on positioning and gear. A few big lessons (which may or may not apply to anyone else):
1) My seat was too low. I guess I should have listened to Dan Empfield. Maybe some of you remember this thread:
Slowman says Jens' seat is too LOW...
In the intervening decade, I reverted to my old, bad ways and lowered it again. Aaron suggested raising it 2 cm. Hmm. Same as Dan.
2) More drop isn't always better. How your body achieves that drop matters. I went from ~14cm drop to ~10 and ended up with less drag. That's really big, because for me, 4cm less drop also means ~15 watts more power output.
3) Helmets really, really matter. In my case, the difference between two aero helmets was over 100 grams of drag.
4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.
5) Q-factor matters, though not as much as hoped. I switched from ~160 to ~130, which saved ~50 grams at 0 deg; 34 grams at 5 deg; but actually increased drag 19 grams at 10 deg. Maybe some smarter folks than myself can interpret that.