Autotune with version 3.5.7

hi all, i want to preform auto-tune on one of my large quad 6s lipo 29" props.
the quad is using pixhawk 1 by radiolink running version 3.5.7.
my questions are:

  1. any tips on running autotune on these kind of large quads, which aggressiveness should i put??
  2. if i update the pixhawk to version 4.0.3 preform the autotune, then rollback to 3.5.7 and just copy the gains’ will this work?

thanks in advanced

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