Here's my RS6 boost log.
<pic>
IDK how it will help though
Well, since this tread is now officially about bragging, I'll play!
Here's mine. Not a "boost log" per se, since I didn't have time to finish the 5120 yet, but a log nonetheless.
Anyways, jokes aside, on subject:
As suspected, the problem was with boost control. Not control lines, though. As it turns out, at some points in car's life, turbos were overhauled. And somehow noone bothered to correctly calibrate wastegate actuators preload. After re-adjusting them, this is what we got. There is still far from ideal, but at least curves look synchronized (see attachment, not the plot above).
I guess, we can declare this issue "resolved" and move on to the next one I'm having with this car in
this thread.
Thanks for all the input!