Out of the box, the Surface Book with the Nvidia GPU is not as fast as it could be. I've been frustrated with the speed with which it does things like spotting and stroking with the pen. Often the non-Nvidia graphics chip (the "integrated graphics") has been faster.
The key is to download the full GeForce Experience control panel, rather than the more simplistic control panel. This gives you the full range of options to control the GPU's performance as shown in the video. The one toggle that needs flipping is to flip the power management from Auto the Maximum Performance for apps where you want to use the GPU, such as Lightroom and Photoshop.
For me at least, this has made a significant difference to the overall speed of Lightroom, and I'm now much happier at plumping for the i7 model with the GPU.
What still hasn't been fixed is the ultra slow scrolling with the touchpad in Grid view - this appears to be an Adobe bug specific to touch devices, however, rather than an Nvidia issue.