I've had an '08 3.0 TDI S-Line Quattro Avant since August and I'm loving it. It's standard in the engine department, so whilst it may not have the out and out performance of your previous models, it does have great mid range pull which makes it feel quick without trying.
You need to try one, but I dont think you'd be dissapointed.
As for fuel consumption, I've copied a reply I posted to a previous thread below as it's relevent:
"Real life figures I'm getting are 37mpg on a combined average, but generally 40mpg if it involves motorway runs (keeping to 80).
I do drive quite "enthusiastically" to come by these figures, so I don't think you'd see much less... if the tanks low and I just tickle it, 45mpg is possible, but that defeats the point of picking the V6.
I do a mixed commute of 30 miles, generally 25 minutes urban, traffic lights queuing etc and 20 mins motorway and get 39 in the morning and 41 in the evening (think thats because the motorway section is biased to one end of the trip and it prefers to hit the motorway sooner rather than later as it warms up quicker)
Don't expect much more on longer runs though, on a recent run from Manchester to Southampton and back in a day I managed 41mpg on the way there on crusie (79mph) and nudging 43mpg on the way back at similar speeds without cruise interestingly.
Having had a 1.9tdi B6 Sport. 2.0 tdi B7 S-Line and a B6 2.5tdi Quattro Sport before, I'm very happy with the figures and the turn of speed. The only time the guage really takes a noticable hammering is if you get stuck in standing traffic (its clear where the stop/start system gains come from) and if you push much above 80.
I'm finding an £80 fill up goes 450-500 miles"
The newer model you're considering I can only imagine eaks a little more from the tank. Oh, and it doesn't use engine oil either, which can be costly these days
Hope thats some help,