I use a lot of layers, adjustments, masks, and large brushes, but that's mostly it
LOL, those are very compute-intensive operations. That's basically saying "I need the most powerful computer I can find" to run Photoshop.
It's hard to generalize an answer to your specific question, because not all GPUs or systems are created equal. If I had to generalize, I'd say you should try to avoid DUAL GPU systems, in which an Intel and some other brand are combined to try to deliver power saving and high performance capabilities. Photoshop traditionally doesn't really like that kind of arrangement, and forum members often advise folks with dual GPU systems who are experiencing problems to just disable one of them (usually the lesser one) anyway.
Keep in mind that a laptop isn't going to be able to achieve as good performance as a desktop for a resource hungry application like Photoshop, yet will be more expensive. You really will want a high-end machine (possibly even mobile workstation class) to paint in the manner you describe.
I invite others who use modern laptops to chime in here and relate their actual experiences, as well as provide information on their specific configurations.
Oh, and I almost forgot... With a PC laptop an advantage of the PC environment (the ability to download and install new display drivers yourself) can be reduced, as many laptop GPUs can only be operated by drivers released through the laptop maker, and not nVidia.com, AMD.com, etc.
In everyday terms, this may mean that down the road a version of Photoshop will be released that won't be able to run on the laptop because of a display driver deficiency, and you won't have the ability to get new software to fix it, thus rendering the machine unexpectedly incapable of carrying you forward.