Basically, if you have a Talent for something, the limitations that face normal channelers don't apply to you, so the restrictions based on raw strength, training level and flow affinity are trumped by your Talent. Even then, a high enough level of training with a weave may lead to results that border on the level of a Talent, as in with Berowin for example. We actually don't know if she has a Talent for Shielding, only that she practiced that weave and is extremely skilled with it.

This is why I think RJ was very insistent on the idea that skill/training was extremely important. The Forsaken were finely balanced because they came from a time when the level of training for channeling was so high that most of them literally were evenly matched, despite differences in Talent, strength in the One Power and temperament.