The M45 has been very reliable, but not as much fun as my last car, a 2002 Audi S8. This week I added the Stillen cat back exhaust...I really like the sound of the exhaust a very mellow deep throated sound that is not at all harsh. It is not any noisier in the car than stock except if you romp on it, then just a nice sound.
I also added an R2C intake unit.
I was traveling this last week so I gave the car to my shop to flush the transmission (~46k) and add the exhaust and intake. Nice ride home from the airport. I really can't feel the increase in performance but suspect that between the two it should be about 20 HP.