You will constantly be doing Real-Time Playback, so you should really consider upgrading your Desktop instead of getting a Laptop, especially as you're planning to use it docked on your desk most of the time, for the following reason:
Any Laptop with a good enough cooling system - that won't get annoyingly loud when constantly under load - is barely portable anymore and thus I don't see the reason why you would get a Laptop for your animation work.
If want have to work at other places and they have good internet, consider using a Remote Desktop Solution to access your Desktop at home as well.