[Kurfürst]

George described it perfectly, this is basically as how January 1944 Messerschmitt AG papers describe the present 109G variants in detail.

G-6 : Jäger
G-6/R1 : JaboRei (the funny three legged version)
G-6/R2 : Jagdaufklärer (Rb 50/30)*
G-6/R3 : Gawähltaufklärer (Rb 75/30 + 2x300 lit droptanks)
G-6/R4 : Gawähltaufklärer (Rb 50/30 + 2x300 lit droptanks)
G-6/U1 : Jäger (Messerschmitt P 6 propeller)

* GLC datasheets also note MW 50 boost for the /R2

This is so far as the Jan 1944 Mtt AG list covers them. Others, from various sources

G-6/R5 : Jagdaufklärer (2 RB 12,5/7x9 or 32/7x9)
G-6/U2 : Jäger (GM-1)
G-6/U3 : ?? Forgot what this baby did.. I believe intitial designation for Jäger with MW 50 boost..?
G-6/U4 : Jäger (MK108)

G-6/U5 and
G-6/U6 were IIRC the ones equipped with MK 108 gondolas, and one of them also replaced the hub cannon with an MK 108.
Jäger (MK108)

The twin droptank versions were very much real, just lesser known.. IIRC something like a hundred were delivered to the units.