When adding layers, I've found it's important to buy tights and kneewarmers that have an articulated knee. This helps maintain freedom of motion in the knees, and eliminates binding across the front, and bunching in the back.
This is great information. I've got a set of wind-front tights. They do the job, but as you mentioned, they bind the knees in the front. What brands of articulated-knee tights and leg warmers have you tried that work well?