Your diff will be a 2.92 ratio. Going numerically higher will give better acceleration. Most people with VE autos go for either 3.27 (HSV A6 ratio) or 3.45 (Holden VE M6 ratio). I put a 3.45 in my A6 ute and love it - pulls away from roundabouts etc much more readily. Someone on here tried their A6 at the drags with different ratios over time and found HSV seem to have got it right i.e. produced the best times. Not an apples for apples comparison but I had an SSV sedan with stock 2.92 diff and basic bolt ons it managed a best of 13.17 down the quarter. My slightly heavier SSV ute with very similar mods and virtually identical power did a best of 12.83 at the same track.
Some people with the A6 even go to 3.7 (HSV M6 ratio) but many people think that's gone too far the other way as it makes 1st too short. Obviously your cruising RPM will change. Mine went from about 1500rpm at 100kmh with 2.92 to a bit over 1800 with the 3.45. Minimal if any effect on consumption, even at highway speeds. You may even find a 3.27 or 3.45 improves consumption around town because the motor isn't having to work so hard to get the big heavy car moving.
Have they tuned your A6?