Even when M3 is broke, I do stop start around the lanes on my 25/30 mile commute, never once had it that low.
Easily mid 50's - Low 60's in the summer
You don't need to justify your
mistake purchase to me (or anyone else).
As said, I know what a 2.0TDi A6 returns for me. I suspect a Passat is no different, unless you bought it from Imber Enterprises, in which case a Ferrari won't keep up, and returns 200mpg.
and yes it's more comfy and faster and less noise at speed. I do drive both quite often you know 
Many a time arrive home in the CC, then jump in 3.2 to take MrsT and Little MissT out. Direct comparisons.
I guess comfort is subjective, but you once said a Plod spec Volvo was the comfiest thing on the planet

. Certainly I didn't find a Passat comfortable for any length of time. More comfortable than a Zafira-A, but less comfortable than, say, a base Insignia which I took to South of France and back (the long distance comfort factor on that was a real surprise, as initially I thought I wasn't going to get settle in the seat). The MFL MV6 leather is pretty hard to beat, based on a 15hr non stop (ish - stopped for lunch, and comfort breaks) drive. But I maintain the pinnicle of comfort of any car seat ever is MFL Elite cloth. Not even a Citroen DS can match the comfort of that.
As to noise, I'm guessing your tappets haven't improved on the 3.2? I reckon, despite the recontoured mirrors, the PFL is better for windnoise than the FL - certainly my MV6 and my old TD created virtually no wind noise (though the TD did make tractor noises), and Goldie and TBE do. The biggest source of noise from the Bullet is those Valtek injectors mounted on that metal plate, and some tyres.
(The biggest source of noise from TBE is the disco she has in the car

)
As to being faster, it may accelerate better in higher gears, but a V6 will be quicker between any speeds anywhere up to 130mph (by which time I suspect the VW has run out of steam anyway) as long as you are in a suitable gear. That's the difference between petrol and diesel.