I thought the rx-8's were supposed to get an estimated 35Mpg off the lot.
I have an 83 rx-7 and I get max 400-450 a tank on the highway but I think I have a dent in my gas tank cause I'm never putting the full 63 Liters in there. Only about 50-55. 250-300km a tank in town. I was working in Canada and used to drive that at $10/hour jobs until the gas prices went above a dollar per liter.
Wait for the new rotary series to come out. They're changing the renesis engine housing size and shape to get more low end torque

among other things.
There are rumors of either a new rx-7 or a budget sporty rotary sedan. IMO they need a rotary more affordable than the RX-8's to keep the rotary enthusiasts happy and keep the rotary community growing. There's also the RX-8 hydrogen hybrids being used in Japan and Europe.
Strangely I seem to get consistent fuel economy whether I drive like a grandma or like a maniac. You get more power / gas used at your high rpm's in these cars so it evens out, at least in my 83.