I can't say that I can see a difference in mileage with/without my panniers.
KLR 650 (Kawasaki KLR 650) | Fuelly
The way the bike handles 75+mph speeds is vastly different but on paper it seems negligible. I prefer to not have them as that a wobble develops with headwinds/passing trucks/speeds over 80mph when the panniers are on, but then I'd have vastly reduced space for road-trip essentials.
![](http://i1002.photobucket.com/albums/af145/star_deceiver/RockyViewNo44-20120630-00294.jpg)