I realize this is an old thread but maybe someone will find it looking to do the same thing. I have a Honda XR 250 dual sport with full-on off-road knobbies and anything bigger would be a waste. I ride to work every day and have ridden from Hanoi to where I live twice (5 hours). The speeds are just not high enough to justifiy anything big. There's some back road areas where I hit 100kph and it feels like i'm really going good. FYI, I'm a former road racer that's done 180mph on a superbike. Just save your money and get an aircooled 250. Motard if you don't plan any off-road stuff. The suspension will be great on the messed up roads that exist here.
A liter bike would be ridiculous and I love sport bikes.