Thanks to ULEZ this is my choice back into a RWD, which fits some of your list.
Large saloon Medium saloon
RWD
Auto
200+ BHP 300+bhp
£10kish for sub 10yr 100k miles example
40+ mpg capable day to day
I think its a little small for me, maybe I should try. But I personally find 5 series causes me issues on longer runs, can't see the smaller ones being any better as they tend to be too taughtly sprung, even in comfort modes for those that have that function.
Clearly large petrols NFG to me, I can't achieve those sorts of MPG figures 
. But the diesels are every bit as quick in reality, if dull, and I couldn't care less about ULEZ 
You can see on the long run, I was not hanging about. Soon as it opened up, so did my right foot.
Suspect it's not for you, it's quite low. You fall into it a bit, quite a difference to the daddy bus. I find the ride firm but good, but I do have a generally good road surface. As it's M3/M25/Great West Road for me on my commute.
Interested to see how normal tyres change it.
I do feel like it's about as close as to your old MV6 as you can get. Interior has worn well, feels like new, dark leather with M-Sport seats also sealed it for me. Those leg extending supports make it very comfortable for me.
I've had the entire family of 3kids + the wife in there and it's been fine. So not sure why you would struggle for size!
That said behind me there little leg room.
