Some questions about building a new system?

I have a couple of questions about building a modeling/rendering computer dedicated to Blender.

My question is mostly about the graphics card and performance.

What is the best or better class of video card to go with. Quadro? or GeForce? I don’t of course mean the best card itself, but the best class of card, since there is a huge range in each class.

The next question is about cost. After determining the class of card, is it standard to think, the more expensive the better, or is there a consideration to make when balancing out the video card, let’s say with the cpu? All this is mostly regarding a single system for rendering and modeling.

The last question is what I hope gets the most answers. What is a really good spec for a graphics workstation dedicated to Blender. I mean everything that you can think of that should go into a system. What are some of your specs.