I will sacrifice a few MPG’s for a well running engine. Glad you are doing well with the 0w40, I know my G35 likes it.A quick update:
M1 0w40 is doing nice in the 2 VQs. In the 2011 MPG didn't change a bit and stayed at 21.6mpg (compared to PUP5w30)
In the 2009, it's ever so slightly lower (may be 0.5mpg at most) sitting now at 22.75mpg with same routes and driving pattern (and even maybe more idling and warmup times with the lower temps these days), PUP5w30 gave me 23-24mpg.
All calculations are manual with miles driven divided by gallons pumped at the pump.