German range tables give the following speeds for the different 109 variants at maximum range conditions, with a single droptank.
Maximum range of Bf 109E-7 with droptank was 1350 km, endurance 3h 50 min.
Maximum range of Bf 109F-4 with droptank was 1660 km, endurance 5h 15 min.
Maximum range of Bf 109G-2/G-6 with droptank was 1700 to 2000 km, endurance 5h 20 min to 6 hours.
Without droptank, it is given as 990 to 1160 km, endurance 3h 5min to 3h 25 min.
(Different documents give different values, probably under different conditions specificed)
From this, for the two droptank version (LR recce variants used this configuration), roughly 2600-2900 km range seems a reasonable figure.
I know of no maximum range table for the 109K, only under maximum cruise conditions (585 km); . Some conlclusions can be drawn from these datas, as the K-4 is listed as with ca 6% greater range than the 109G under maximum cruise conditions, probably down to increased aerodynamic cleanness and/or more efficient powerplant (higher CR motor).
In addition, the 109K had the ability to carry 118 liter (+29,5%) more fuel internally in its rear aux. tank - in this case MW50 was not carried (it used the same tank).
I`d say the 109K-4s maximum range was 1850 - 2100 km, and could be extended to something like 2100-2400 km if the rear tank was used an aux. LR fuel tank (and no MW 50 carried. However with C-3 grade fuel the performance would be similiar as with the lower grade fuel, MW-50).
Messerschmitt Bf109F-4 Range Table