I have been very impressed with the capabilities of the Mashima 9/16 motor especially once the magnets have been chopped down to size as required for some of the Fence Houses kits.
Here's a short video of a J27 chassis I'm working on, it hasn't run in 4+ months, hasn't been oiled, is only picking up from the tender and I didn't clean the tender wheels prior to recording the video. At one point I turned the controller down a little too much and you can see the motor briefly stall.
There's still work to be done as there's a couple of tight spots but I'm very happy with how things are going.