the powerchip only advances timing by a few degrees. it doesnt change your fuel maps at all, so extra performance is minimal and could be achieved by advancing your distributor.
i have had people comment that the antrx chips increase fuel economy, which doesnt suprise me as it pulls a lot of fuel out of the map as the stock maps are tuned super rich, but ultimately it depends on how you drive. if you're just doing highway km, you could easily get 650km out of the tank and still have a few litres left, you could potentially get more than that its been a long time since i've driven a u12 to know, but then at the same time, you could drive around town like a bit of a goose and you'll only get 400km out of the tank.