Starting SpecsTo start off with, both the Surface and the Book have pretty nice starting specs which I know will run Photoshop smoothly. The processors are even better than the previous models! Though I'm still undecided if I need the hot keys that the Cintiq device would provide. The sliders and hotkeys on the Cintiq are useful for quickly zooming in and changing brush size, but are they worth the extra expense?
Subtle ImprovementsThe Surface Pro 4 seems a nice improvement on the previous model in subtle ways, as it now has a much improved stylus with a purported 1024 levels of pressure sensitivity as well as an eraser that actually erases, which it didn't have in previous models. The representative also told me that the stylus comes with interchangeable nibs by default so you can change the resistance of the stylus if you want. The Freshpaint program that comes with both the Book and Surface also seems to work very similarly to Corel Painter, which was a surprise!
Differences Between the Book and SurfaceThe Surface Book is much like the Surface, except that the Book's screen is a couple inches bigger and has a hardier keyboard, though I felt that both keyboards were comfortable and could probably replace my laptop as far as typing if I actually wanted to use either one to write while I'm out as well. The Book, like the Surface, also disconnects from the keyboard to become a standalone tablet.
Extra StuffThe Surface has one USB 3.0, a micro SD slot, and a mini displayport, while the Book has two USB 3.0 ports, a full sized SD card slot, and a mini displayport. These will be handy for plugging up extra hd's or devices.
PriceThe Pro starts at $899 while the Book starts at $1,499 (with the Cintiq Companion being $2,499 by comparison).
I'm hoping to save up and get the Book if I can, but I may end up settling for the Surface. Either way, I'll be sure to come back with a full review once I've had time to completely settle in with either of these devices!