All of the ones I have seen run like an old Tyco. They look great, but require a re-motor to even think about DCC or to run good.
Actually, a properly built Tyco Pacific or Mikado can be a very smooth running loco and will outpull many recent plastic steamers. Of course, even these will benefit from a can motor, but there are brass models out there, with open-frame motors, that might astound you with their capabilities. One that springs to mind is the CNR Northern (the exact class escapes me) by Toby, with excellent low-speed control and great pulling power. Conversely, the CNR K-5-a, imported, I believe, by PFM, was a great looking loco with a good-quality can motor, but had all of the running characteristics of a one-legged antelope.
I have a Key USRA Light Mikado in my shop now, for fresh paint, which is equipped with a "factory" can motor. It's a smooth runner and pulls well, and I believe it was built in the mid-70s.
If you like the loco, and it's of an otherwise unavailable model, I suggest that you buy it. Almost any locomotive can be made to run well, although some may require the outlay of some serious cash. Others merely require the attentions of someone willing to "tinker" with the mechanism. The K-5-a mentioned above underwent extensive "tinkering", and now runs extremely well.
Here's one of those Tyco Mikes (sorry, but I don't have a photo available of the other locos mentioned):
Wayne