I have heard (via a close friend, ex-TWA F/E) that typical cruise for R-2800's in Convairs or DC-6's was full low RPM, full open throttle (at altitude there was no worry of overboosting the engine).
We used to cruise an R-985 (on a Howard DGA) at 1650 RPM and 26"Hg MAP - this gave good fuel economy, quieter cabin, and less than 50% power for longer engine life.