Highly recommend the ADV flicks "Long Way Round" and "Long Way Down". I can't speak much to ADV riding, but if I ever did a serious trip, I'd do it on a BMW GS.
Yes, great films ... but I would not follow their ADV travel template exactly. Remember, they were total off road Noobs to start, and had never traveled on the road for months at a time.
At least Charlie had sense enough to know that KTM was the bike they should have started on. Not to be.
KTM rejected them, as both were too inexperienced and likely would give KTM a bad name. (said KTM ... big mistake on KTM's part!!) They were rejected even offering to PAY for the bikes. They got the BMW's free. But suffered mightily for that decision.Remember the shots of Ewan crying in Mongolia's mud?
Reams of posts about "which bike" over on ADV Rider. The current trend has more and more serious travelers doing "serious" rides aboard smaller and smaller bikes: 450's, 250's,... even some 125's.
Once out of USA this starts to make sense. I'm getting older and weaker now, so headed from my trusty DR650 (about 420 lbs. fully loaded with RTW luggage and full tank) My next bike will be a WR250R. I'm pretty sure I can knock 100 lbs. off that DR650 figure and carry nearly same load.
My DR650 has over 60K on it, been to Mexico, five major trips. Mostly Baja,
about 50% off road. Also, quite a bit riding mainland Mexico.
Also ridden my DR out to Utah and Colorado on month long rides. It's quite capable both ON and OFF road.
I've owned XR's (600, 400, 250 and XR650L),2 KLR's, XT600R Honda. Of all dual sports, the DR650 is the BEST in my experience.
I raced off road AMA Enduro (B rider) 8 years in 80's/90's. All 2 strokes.
After AMA retirement got more into road based ADV Touring with my DL1000 V-Strom and Triumph Tiger 1050. Vstrom great, Tiger good on road but a NO GO off road for me. (I'm too short)
I"ve ridden ALL GS's extensively ... love GS's but would not trust one going RTW. They break, things fail. For last 20 years I've ridden with group of hooligans ... for about 10 years it was mostly all R1200GS's. Only KTM had a worse reliability record among our group of 60 experienced riders.
KTM"s got better ... and still better. But for travel, it's a totally different world and other things must be considered. In the end you could say .... "run what you brung". But if you can choose .... take something proven, smaller, lighter ... cheaper and expendable.
The DR650 is the most reliable single on the market today. It's also dirt cheap and SO EASY to self maintain. Super tough. Not bad off road within reason (with a few mods) and great cruising at 70 mph all day long. (better seat a MUST)
The GS would be GREAT if you truly stay ON Tarmac. Dirt roads OK, unless MUDDY! Deep sand? Sorry, no GS for me. To go exploring along the way ... then a 250 may be better. 650 class OK too if set up right and you can ride.
If you're at Jimmy Lewis level ... take a GS or big KTM.
I'd rather wear out my $4K DR650 (used) than a @20K BMW or KTM 1290.
Before doing RTW, do a long Baja ride as a shake down ... see where you come out and find what works for you.