(1) discover if your 3D modelling software has GPU acceleration (opencl, cuda, openAcc, etc). If so see what graphics cards accelerate best and buy a laptop with that card.
(2) discover if your 3D modelling software is good a running multi-threaded. If so get at least a quad core.
(3) decide how often you will be running on battery and how often you will be running off the brick. I've seen people at work trying to carry around laptops with 170W bricks that must weigh pounds. I get 4-6 hours w/o recharging. Then choose between efficiency and performance.