Thanks people. I guess the main reason I was using so much fuel was it was quite windy and I was at WOT quite a bit to compensate. I have ordered a JEN .56, I should get that in a few weeks when the delivery comes in. I can't wait!
Paul at Just Engines reckons that I should need a 4 or 6oz tank for .56 . . . but I'll see what happens with the current tank. The engine develops nearly twice the power of the 40LA so perhaps in use, the engine may even run for longer as a lot less throttle will be required. I shall test it anyways before I take the plane up and put a larger fuel tank in if needed.
Thanks again for the help, people.