the last is interesting in that it starts at low rpm and boost never overshoots but the two prior that start at a later rpm do. What's the recommended way to counter that?
Tune Q2... now, Q2 is a tricky beast, pay close attention to the axis...
The RPM axis is clear: if you get different overshoot depending on RPM position, vary Q2 with RPM
The other axis (lde, iirc) is not so clear: it allows you to schedule the Q2 gain depending on lde; that is to say, you can make Q2 bigger or smaller long before actual meets requested, or JUST as lde nears zero..
But the D component from Q2 is already proportional to how "fast" lde is changing (e.g. spool), so counter intuitively, if you have a lot of overshoot on fast spool, but not slow spool, you may want to increase Q2 for LOW lde.
Conversely, if you have overshoot on slow spool, but not fast spool, you want to DECREASE Q2 for LOW lde.
You can move the whole thing up and down by toying with IMX, of course. Typically, it is easier to just make IMX very conservative so you dont overshoot, so you can keep Q2 low. You might give up a bit of spool, but it is likely better to have undershoot than uncontrollable boost oscillations (which you will ALWAYS have on overshoot.. that is the nature of PIDs).
Now, keep in mind that on top of this, you also have the IMX trims going on.. but if lde is never that big for extended periods of time, the ECU should not be trimming IMX much.
