Yes, the revs/speed factor is fundemental when it comes to mpg. The higher the revs, the more fuel will be used over a given distance.
Over here in Jersey, a small island 9x5 miles, with a speed limit of 40mph, the best mpg i've had is 58mpg, with an average of 54mpg. I use the bike every day to get to work, to get out to jobs, and getting home and to the shops. For a period of 2 months last year, I visited the same petrol station, kept my fuel receipts and made a note of how much fuel was put in and the mileage on the odometer for eash visit. From that information I was able to work out a precise mpg.
In top gear at 40mph, revs are at exactly 3k. But because of the small size of the island, there's a lot of stopping and starting, and so i don't get to cruise at 40mph much! If I could cruise at 40mph for a few hours, I reckon I could easily attain 65mpg+
The next time I take the bike over to france, where cruising at 55mph is easy on their national routes, without stopping and starting every two minutes, I'll take note of fuel consumption and mileage, and see what mpg I get.
1980 Honda XL250S
1980 Honda XL500S
1980 Yamaha XT500G x2
1979 Honda CB750F2
1998 Buell S1WL
2005 Suzuki DL650 V-Strom