The book 'Heinkel He 177, 277 274' by Grielh Dressel talks about there being doubts that the He 277 could live up to that 4,900ml claimed range potential.
I guess we'll never really know for sure.
The Heinkel 277 would have been a great performer with 4 DB-604c or Ju-225 engines with a 2 stage or in the DB-604 the D that was to be a 3stage.Using the DB-628 design stage two design.
If the Jumo 211 powered He-177B had been produced I assume it would have been superseded by the He-274 if/when DB603 or Jumo213 engines become available. Just as the Jumo 211 powered Ju-88A became the Jumo 213 powered Ju-88G.