On this one, I too concur with Mr. Lester!
The loads you describe are perfectly suited to the 1894 Marlin. Although not as strong as a Win 92, or copy thereof, or a 336 Marlin, they will still handle any load that is listed anywhere for the Blackhawks or Contender.
I have rutinely fired a load using:
BTB .452"-310g WLNGC/23.0g H110/WLPP/Starline Brass/1300 fps in 5.5" bbl.
This load picks up about 225 fps in the long barreled cowboy gun, and really has authority. It in no way stretches the limitations of the 1894 action. It will eat a diet of these day in and day out and with superb accuracy I might add!
The cautionary advice is well given, and should be received just as well. While true the Redhawk will take a mite higher pressures than will the other guns, it is best not to go into the realm of potential disaster by pushing the envelope. However, the loads you describe should be just great daily fodder for your Marlin!
My very biased opinion FWIW
God Bless,
Marshall