Oh, the ongoing 990 Adv vs. F800GS debate.....The 990 Adv is 65 pounds heavier (456 lbs dry) than the 800GS (392 lbs dry). I'll take the 800GS, please. And that's one of many reasons why I did! 65 pounds is a BIG deal off-road. Besides the fact that the 990's (and most KTM's for that matter) look god-awful fugly.
Besides. When you compare bikes, you compare the 990 Adv and the R1200GS. Those two bikes are in the same weight/power/market class. Not the F800GS.