The biggest hardware progression I’ve seen recently has been rendering engines’ inclusion of the graphics card’s processing power. I recently made the switch from Vray for Rhino to Bunkspeed Shot partly because of this (though I think the newest Vray can use the GPU), and I haven’t looked back. Software developers are optimizing their engines to work best with the tech being used in gaming GPU’s (notably NVIDIA’s CUDA architecture) so there’s no longer a need to go with the ridiculously overpriced Quadro line. A solid GTX or Titan card will produce far better results for a fraction of the cost, and an SLI system (two bridged cards) will fly.
That being said, I haven’t rendered on a laptop in years. I moved away from it a while back because it was just killing my machines. I would go through a Dell Precision every 1.5-2 years. I’ll second the previous comments to say that, if you can figure out a way it works for you, a desktop really is the way to go. Take a look at some of the custom gaming pc builders out there. You can get some awesome rigs put together pretty cheaply (my personal recommendation is Maingear.)
Hope this helps.