If Cu and Pb are elevated one could suspect bearing wear. In your case Cu is up but Pb is zero and Fe is normal, so their "don't worry, we'll watch" and "turbo" comments make a lot of sense I think.
M1 seems to have done a good job. I use it without worry in one of my cars, and used to use it in two.
EDIT: Just noticed and thought about this: You have correctly gone to 5K for an interval (anything less is just old-fashioned IMO, Subaru should be ashamed to have ever required a 3750 from anyone in my lifetime, shame on them). The averages stated are for 3,900 mi intervals though, so you went ~28% longer than average; your Cu would have likely been lower had you gone only the average interval (how lower I don't know, but you see what I mean).
It is also very, very interesting to see that the viscosity is correct despite using the M1 that so many nasiocers have emphatically stated shears down unacceptably and leads to engine failure. One explanation is that the oil shears initially and then viscosity increases with age (this is in fact seen in M1 0W-40, with which I have had good results and so have the poor souls with modern VAGs and Porsches). Another explanation is that M1 does not lead to engine failure due to shearing, but I don't think that's a point that can be argued effectively at this stage, as it ends invariably in a shouting match "over there" and few are willing to let the data get in their way etc.
Thank you very much for posting your data. The more the merrier.