A bit jealous of you 500 owners - sweet bikes they are!
I get about 40 mpg on my '10 'Berg 450 in normal trail riding. It would probably easily do 50 cruising on the street. I have gone 100 miles off road on it's 3 gallon capacity. The 500 has a similar FI system, so 35 on the trail and near 50 in smooth dirt road/street riding sounds right. They are reasonably efficient, feels like every molecule of fuel is being injected and burned correctly. The FI really does feel different and better than a carb.
2010 Husaberg FE450 (plated)
2006 Yamaha FZ1