Not a fair comparison because we all know that women are digital when it comes to throttle use (full on/full off) 
Lets see if any female members on here take the bait to that one!
Very true IME.
I always wondered why Mrs. KW's MX 5 struggles to manage 30 MPG until I did quite a bit of driving in it over Christmas and averaged 38 MPG.

Especially in a heavy car, it all depends how you drive it. There is the potential to waste a lot of energy accelerating 1.7 tonnes to speed then stopping it. If you plan ahead in your driving and don't pour energy into accelerating the car only to have to brake 200 yds up the road it makes all the difference.
Interestingly, my Westfield (totally opposite situation. 650kg, manual and cr@p aerodynamics) returns approximately the same fuel consumption regardless of how it's driven (within reason) or in what type of traffic.
As long as you're able to keep up 45 MPH or more in an auto V6 to allow lockup in top gear (increasingly difficult on the roads round here

) they are pretty good. There are a few more moving parts in a V6 and a bit more weight, some more pumping losses as it'll be more hevily throttled back during cruising. Then again, they're slower revving. :-/
When I bought mine, I figured that there was so little in the fuel consumption outside the urban cycle that a V6 was a no brainer. It's only really in stop-start urban traffic and short journeys that they suffer.
Kevin