Bachmann's N scale 4-8-4 has at least two variations. Check the side rods.
Bachmann sold 4-8-4's in sets and individually. These had either black plastic or metal side rods. The black plastic units did not perform as well as their metal counterparts. Most of the 4-8-4's that Bachmann sold individually had steel side rods. These performed much better.
I have quite a few of these units, both plastic and steel side rods. They all run pretty well, but overall, the steel rods run better. Both are sometimes touchy about electrical pickup and they prefer smooth track. They will perform on 9 3/4" radius curves, but don't like it much.
Bachmann still lists these in their catalog at around $100. (http://www.shopatron.com/product/product_id=BAC58052/211.0) They should be heavily discounted elsewhere and you can buy them inexpensively on eBay. The newer ones probably will outperform the older one because they've been in production so long that most of the bugs have been worked out.
Discounttrainsonline lists one for $65 http://www.discounttrainsonline.com/N-Scale-Locomotives-Bachmann/N_LOC_160_2.html
eHobbies lists the Empire Builder train set for $145 (http://www.ehobbies.com/bac24009.html). It looks like these have metal side rods now.
I wouldn't hesitate to try a new one, especially at $65. It sounds like a good bargain. If you like them, adding to your loco roster is easy on eBay. Just do your homework, read the descriptions and ask questions if necessary.
Hope this info helps. I like my 4-8-4's. When I figure out how to get them all converted to MT's, they will look great doubleheaded!
Darrell, knowingly quiet...for now
Darrell, quiet...for now