I checked my logs and did a quick median calculation and it looks like the 2.5's are averaging 22 in city and 29 highway. That includes the 2 98 GT's and 01 Forester S. The gas mileage on the Forester stinks and has since day 1 (17 city/22 highway). The 2.2L's (98 OBS and 99 Legacy 30th Anniv L Wagon) are averaging about 23 in city and 31 highway. That's spread across two 5 spds and three auto's
BTW - the Audi A6 Quattro apparently requires that split-tank/hump over the drive shaft and has problems with accurate gas gauge readings. IIRC there is a class action suit being filed again Audi because numerous Audi A6 Quattro owners have been stranded when their gauge indicated fuel and they were o-u-t of gas. Audi is trying to resolve the issue.