According to kurfurst.org, the 605DB and DC are the same powerplant, in different configurations,
for use with B-4 or C-3 fuel, or 1,80 or 1,98 ata maximum manifold pressure.
Of course, the Luftwaffe suffered from fuel shortage, and often only a very limited number of aircraft were supplied enough fuel for a mission.
All the later 190 A powered by BMW 801 needed C-3 96 octan fuel as well. IIRC they could not even take off without C-3, in contrast to the DB605 powered 109.
My point is, if there is enough C-3 fuel for 190 A-4 to 190 A-8 to take off, there is as well enough C-3 for the K.
--= Bf 109K-4's =--
The MW50 WEP has been reduced from 1.98 ata to 1.80 ata. This since the absolute majority of Bf 109K-4's used B4 fuel and not C3 fuel during their service. As such both Bf 109K-4's have had their engine setup rebuilt from the DB 605DC to the DB 605DB engine. This results in ~10 mph loss at Bst2, but the K-4's gain ~5 mph at lower altiudes, at Bst1, due to better low alt power output when using manifold pressures at 1.45 ata and lower with the DB 605DB engine.
the DB 605 DB and DC designations, as noted in the above datasheet, referred to the same powerplant, in different configurations,
for use with B-4 or C-3 fuel, or 1,80 or 1,98 ata maximum permissable manifold pressure. Conversion of the DB and DC powerplants
was a simple matter, and could be performed with a simple screwdriver. The DB 605DC configuration could be set for either 1,98 ata
or 1,80 ata 'Grundeinstellung', or 'base setting' maximum manifold pressure. In the former case C-3 fuel was to be used with conjuction
of MW-50 injection. In the case of 1,80 ata Grundeinstellung, C-3 fuel could be used without MW-50 injection.