When I replaced my BMW F650 Funduro, I went through the same questions. I also compared the XT660R. F650 GS pros: - Huge resource in www.f650.com - Motor is known to do high miles. Relatively few weak points (e.g. water pump). - Lots of accessories - More fuel efficient than other 650s including the Peg (Peg is still very good) - Slightly
Given the early GS clutch problems and G650GS manual notes, semi synthetic JASO MA oil seems best. 2016 Update. BMW changed their oil supplier from Castrol to Shell, they now use Advantec Pro SAE 15W50 for the 650GS. BMW Advantec Pro SAE 15W50 is semi-synthetic and meets SAE API SM, JASO MA-2 specifications. BMW F650GS, Dakar, G650GS and SertaoSan Francisco. I couldn't find any clearance specs either on my F650 when it arrived, so I measured: Unsprung: 24cm (9.4") Settled under its own weight and panniers: 19.5 cm (7.7") The 800's seat is 6cm (2.4") higher with an identical frame, so you can probably add that to the 650's dimensions for reasonably accurate clearance measurements.
The 2001 BMW F650GS had installed underneath its fairing a 652cc four-stroke single-cylinder liquid-cooled engine fed by an electronically-controlled fuel injection system, delivering 50 hp with B7j2.