I own a 03 and 04 450, and have access to a 07 450.
The 03 and 04, I run at +38 to +42. This is seat of the pants and plug tuning. I can tell a difference in the way the 04 starts if I move out of that range. Some say the trim dosen't effect the starting, maybe on paper, but in real life it makes a difference.
The 07 I still don't know, it showed up -60, and didn't start very easy, and seemed to be under powered. I trimed it up to 0, and it starts much better, and it has nice snap. I have the Technoresearch software.