Hi Brian,

You're right in that the A4 is a bit on the small size inside. Like the BMW 3 Series and Merc C-Class, they're designed around the front seats not the backs. If you want a car of that sort of size but with decent rear seat space, you need to look for more mainstream brands - Mondeo, Mazda6, Superb, Avensis, another Passat and so on. 

 

The good news is that you're wrong about the A6. It's actually hugely economical. I recently drove the updated A6 Ultra 2.0 TDI and got 65mpg on average. OK, so an older non-Ultra model won't be that good but 50mpg should still be pretty easy. Heck, I've managed to squeeze 45mpg out of a 3.0 V6 TDI quattro A6 in the past...