adjusting for velocity and consistancy FX .30 Impact

I have a question for you folks that do some tuning. I was going to tweek my FX impact .30. I was going to try and change the velocity by 20-30 fps for accuracy and air savings. main thing is shrinking the group size. I am looking for opinions on whether to adjust the hammer spring adjuster underneath the air bottle to get my changes or adjust the regulator. do you folks have any pros or cons or just best practices?
thanks for the responses.