I managed 425 miles or therabouts on one tank. That was running a charger in and sticking to 3k revs for the whole tank, I drove the length of the country on quiet roads so no slowing or speeding up. For normal driving I get about 350 miles out of a tank, thats with fairly mixed driving and I'm not the most economical of drivers.
I think G's when they are all working right are very good on juice, if they arent, there is something amiss somewhere imo.