Sorry SWRR - I can't render an opinion on the MTH 2 rail K4s as I've not seen one close up. Generally, I don't go for diecast steam locomotives for 2 reasons.
- I find that the castings' wall thickness at the cab windows, roof, and tender deck detracts from the model's appearance.
- I enjoy revising commercial models to capture the look of a specific numbered PRR locomotive and find soldering brass fittings to a brass boiler/tender shell the best way to go.
That said at one time I owned a 3 rail K-Line K4s for our Christmas tree layout - positioned next to a Kohs K4s from several feet away it looked pretty good.
For those that would like to dive deeper into PRR K4s locomotives I suggest hunting for an out-of-print copy of NJ International's The Many Faces of the Pennsy K-4. One hundred and seventy-seven pages of photos and text 
. Twenty+ years ago a picture in that book inspired me to modify a Precision Scale K4s to represent 5492 as it appeared in the postwar era. It features the so-called hybrid look - classic original headlight and generator combined with a cast drop pilot. Modeler's note - red cab roofs were no longer standard PRR practice following WWII - not to say there weren't a few exceptions such as locomotives dolled up for fan trips.
