The 800 is about 25Kg lighter than the 1200.
The 800 will do the same distance to a tank as the 1200.
The 800 carries more weight than the 1200.
The 800 is a hundred times better offroad than the 1200.
The 800 is longer and taller than the 1200.
The 800 is harder to lift than the 1200.
Having had a 1200, a 1200GSA, and now owning an F800GS, the 800 is by far the more versatile bike. Unless you're a complete nancy who can't stand a wee bit of wind, buy it.
The 800 will do the same distance to a tank as the 1200.
The 800 carries more weight than the 1200.
The 800 is a hundred times better offroad than the 1200.
The 800 is longer and taller than the 1200.
The 800 is harder to lift than the 1200.
Having had a 1200, a 1200GSA, and now owning an F800GS, the 800 is by far the more versatile bike. Unless you're a complete nancy who can't stand a wee bit of wind, buy it.

brand new 800 or a used 1200.