Factors of adhesion below 4 are often considered undesirable for steam locomotives, and the K5 design did prove to be rather less sure-footed because of it.

They were fitted with Worthington-pattern feedwater heaters, power reverse, unflanged main drivers, and both used nickel steel boiler shells.

As built, both carried their bell on the smokebox front, hung below the headlight; this arrangement was common on other roads but at the time unique on the PRR.

This cast locomotive bed design was a successful trial, and was repeated on 1930s order for 100 M1a class 4-8-2s, as was the Worthington feedwater heater with mixing chamber behind the stack.

The greater efficiencies of this gear gave the locomotive a higher tractive effort of 58,092 lbf (258.41 kN).

Both were updated after World War 2 with the standard front-end "beauty treatment" given to most K4s locomotives: a sheet-steel drop coupler pilot, higher-mounted headlight, and turbo-generator mounted on the smokebox front for easier access.

They proved that building a larger Pacific than the K4s was not worthwhile, as the reduced factor of adhesion limited the locomotives' ability to put their greater power to full use.