Is it possible the copper from the first sample was residual leftovers from the previous oil? Because the T6 looks to be doing very well in that engine.
I'd suggest sticking with a 40 weight oil since turbo Subarus seem to like it so much. T6 is excellent, if you wanted to go for a change up, you could try M1 0w-40, or Castrol 0w-40. Or if you could find them Pennzoil Platinum and Valvoline SynPower are both available in 5w-40 but I don't know anyone who's seen them in stores (might be a Euro oil).
I'd suggest sticking with a 40 weight oil since turbo Subarus seem to like it so much. T6 is excellent, if you wanted to go for a change up, you could try M1 0w-40, or Castrol 0w-40. Or if you could find them Pennzoil Platinum and Valvoline SynPower are both available in 5w-40 but I don't know anyone who's seen them in stores (might be a Euro oil).