I managed to find the output_log.txt which says that the dedicated GPU is in fact being used. It still seems strange that I don't see any performance change when switching between integrated and dedicated graphics, but I guess it could be a driver issue since there hasn't been an official update of surface book drivers so far (although the most recent version of the nvidia drivers install without problem). The poor performance might also be due to the fact that the monitor is very high resolution (3000x2000) and then scales the desktop by 200%. Performance is better when I use windowed mode instead of fullscreen, or when I modify scaling from the desktop settings (it actually runs better when I raise scaling to 300%, although that may be due to it actually running on a lower resolution). It might be a Unity issue with high-resolution / scaled desktops since Dungeon of the Endless, which is also apparently a Unity 4 engine game, runs at about half speed until I lower the desktop resolution to match the in-game resolution. "Fullscreen" in both Dungeon of the Endless and Pillars of Eternity really seems to be more like "Borderless Windowed" in a lot of other games, which sometimes creates problems with scaled desktops.
In any case, thanks to both of you for your help and I'll keep messing with the settings to see if I figure anything out.