I don't think such a chart would be feasible - at least as you put it. The capabilities of 0-6-0's or whatever vary tremendously from model to model and manufacturer to manufacturer. So you can't say "an 0-6-0 will pull X." The train magazines usually will give the drawbar pull in ounces when reviewing locos, which is probably the only way to judge accurately. But again, you'd basically need a chart showing every specific make/model/wheelbase of loco, not just generic.
What you saw at your LHS was probably the recent offering from Model Power called "MetalTrain" - they have cars and locos all made of metal. Heavier cars tend to ride better, derail less, etc. BUT the metaltrain line has taken it to the extreme. Far heavier than the standard NMRA recommendation, and any responsible LHS owner will tell you that they're only meant to be pulled with the "metaltrain" locos specially designed to pull cars that heavy (and currently only available in a few models of diesel). I happen to know one of the guys at ModelPower (they're located nearby) and even he admits these are not meant for pulling long strings of cars, for much of any grade, etc. There are other all-metal cars available, most notably brass ones, but all will dramatically reduce the number of cars a loco can pull and up what sort of grade.
Manufacturers WILL usually indicate a loco's minimum radius. Usually, not always. Always best to ask and use common sense. Radius is USUALLY determined by the length of fixed driving wheels - i.e. an X-4-X will generally go round much tighter curves than an X-10-X. Articulated locos often do better than you'd expect - getting a lot of driving wheels going while handling reasonable radius curves was one major point of the prototypes. There have been more than a few 4-8-8-4 "big boys" that will make 18" radius curves -- but they look pretty ridiculous doing it.
Again, there's no "standard" out there. In my experience, running anything above an X-6-X on 18" radius is not going to work (or if it does, won't work well). X-8-X (no articulateds) is my limit on my layout with 22" radius curves. I have a branch section with VERY tight 15" radius curves, that will only do for the smallest engines (e.g. 4-4-0 "oldie" American style) or locos specifically designed for tight-radius work (e.g. two-truck heisler or shay).
Hope that helps,
Kris
