Just rode from Stoke to Cognac on my Gen 1 Fazer 1000 with Full monty Ivans kit, tank bag, top box and tail pack. Mostly on Autoroutes at an indicated 80 to 90 mph all the way, but mostly 85 (except for the UK with the 50mph limit for most of the M6) and got about 46 mpg, at 150 miles i still had a quarter of the tank left.
I'm pleased with that, if i dropped the speed down to about 70, i would probably get well over 50mpg, but i want to actually get here ASAP.