I recently got lent a new F650GS SE to take Morocco to update my Morocco guidebook. I asked for the 650 twin in particular as I believe it's a better all-round overlander than the 800 or the Sertao: lower and lighter than the 800, tubeless, 19" front, less revvy.
On the way back I had a quick spin on a Triumph Tiger (non XC) - fantastic engine but I'd rather have been on the BM in the desert.
The SE has nothing more than a new 800-like paint job AFAICT, plus a long list of options: main stand, ABS, computer, heated grips. The loan bike I got had all that + BM bash plate, engine crash bars, hand guards + Metal Mule rack, tall screen and rad guard. And best of all - Heidenau K60 tyres.
The '650 'didn't miss a beat in 4000 miles from new - the worst I can say was some surging when the thing got hot while going slow in sand or over rocks with a back wind. Once the track eased up that went away. Don't know if that's normal.
The other problem was the high, road-oriented gearing - in that respect I believe the 800 is better. I expected this and dropped the front cog by one tooth to 16 but it was nowhere near enough to make a difference. On the piste I never got beyond second, but the clutch managed fine and I never needed to adjust it.
Worst thing on this bike is the seat which became so bad I had to buy some foam to get me home from Morocco. After that, an 800-km day was easy. I'm tall enough, but still liked the low seat height for off road paddling and just plain getting on. The MM screen was a couple of inches too low for me, but I'm sure glad I had it.
Average mpg was 68.2, about 5% worse than the XT660Z Tenere
I used for a similar trip 3 years ago, but of course I had a much smoother engine this time. I met up with a mate on a bored-out TT250R out there and one day I was even 10% better than him on fuel. All with lower gearing and baggage as wide as a cart. Worst mpg was 51 spinning and pushing through soft sand at road pressures north of Erg Chebbi and the best was 80 coming off the Middle Atlas in the rain.
Full mpg data is here
Once they wore in those K60s were brilliant on everything from wet roads to dry tracks, even thick bull dust. And at the rate they wear (a third down on my trip) I won't be buying TKCs again.
All things considered the bike was easy to handle on the non-technical, mostly dry dirt you get in Mk. The 19 inch front tyre no problem on the dirt that I could tell and the bash plate hardly got a beating, so it shows you can manage without the 800’s extra height. Partly that’s because the suspension is firm which paid off on the dirt and the road. Only turning on mountain dirt hairpins was difficult - again maybe the tall gearing exacerbated that, or just that even despite the tyres, I was reluctant to turn the 200+ kilo bike like DR350. There’s a full review of the BM plus some of the gear I used on my website