I read a lot about the new beemers, and even heavy duty offroad test of the new F650GS, and it gets a very good review.
The comparison is made like this;
F650GS the 1200GS litte brother
F800GS the 1200GS Adventure little brother
One enduro test they preferred the 650;
as they did not notice any major power increase from the F800GS
The F650GS had good offroad capability, the F800GS was superior
The F650GS was superior on the road vs the F800GS
They found tubeless tires on the F650GS to be an advantage as it's easier and faster to plug a tire than remove and glue a tube
They did not see the spoked/cast wheels to be of major advantage for normal enduro riding
The F650GS accepts any fuel on the pump, the F800GS does not without buying expensive additional fuel map for the then required computer, plus loose power.
Summed up with the F650GS was a great bike for any road, awesome for twisties and had offroad capability to do trail and terrain, the bike to ride every day and do a journey with riding the trail around the mountain. Versus the F800GS was not as good on the road, most difference in twisties. However they called it the bike you ride and take directly over the mountain.
I don't know never tested either, but from reading up on them the new 650 seems to be pretty ideal for what the 650's normally do when it comes to offroad in Asia, touring, doing dirt roads, doing trails, it has a twin and nice power to boot for the journey, adequate speed for touring even on highway speeds. I would take neither on a real offroad journey, then I think a 250 is what you need in Asia, maybe push it to a 400... KTM or something, the 650's are to big and heavy for Asian terrain...
Both of them has 10,000km between services, which is brilliant...
Anyhow the prices are very high for both bikes unfortunately. If the new 650 was around 580k a lot of more buyers would go for it, but 690k is horrible...