The filters in the drop down list of Filter Gallery (that's the vast majority of Ps filters, including Watercolor) do not use the GPU as far as I can tell. They are relics which were designed and coded decades ago for running on a CPU and, even on a modern CPU, they are hundreds to thousands of times slower than the same results created by a modern GPU.
Some GPU-intensive filters are Adaptive Wide Angle, Field Blur, Tilt-Shift Blur, Iris Blur, Liquify, Oil Paint, Lens Correction.
I guess the best question would be: What do YOU expect to do with Photoshop? THAT is what should be fast and fluid on the system of your choice.
- If, for example, you paint a lot of stuff, then you should see how well the Brush Tool works in painting things on an image.
- If you do lots of photo retouching, maybe Content Aware Fill and the Clone Tool should figure in your testing.
- Do you plan to do 3D modeling? If so, then it should be able to create 3D extrusions, etc. with ease.
My advice is to shy away from any system that offers only an Intel GPU, and shoot for an ATI or nVidia-equipped system. Intel's display drivers have traditionally been inferior, and with a laptop you usually get far fewer options for upgrading drivers.
More memory (RAM) is better. Much more is much better.
If I were buying a new laptop right now, I'd make sure it supports SATA3 and spend the big bucks for a huge SSD.
I don't know what your reasons for wanting a laptop are, but if it's a toss-up between laptop and desktop, the latter will generally do a better job of running Photoshop.