I just attach the LM1 logger and floor it in as high gear as possible w/o killing myself.
Then I park, download the log and examine the curve.
Note, this is measuring boost treshold
which has nothing to do with turbo response. Response is a function of shaft inertia. With other words, you can have very quick turbo that comes online late (BB, clipped impeller) or turbo that has lazy spool-up but starts to boost early.
Sounds like an oxymoron but it isn't. Turbo on pic (Mitsu TD05-12G) is one of those that boost early but time time to spool up when "on cam".