So I kinda became obsessed with studying the new wave of tablets out there. At first I got my hopes up about things like pressure sensitivity because of talk about using the Wacom Bamboo stylus. However, those people weren't artists and didn't know the difference.
So I ruled out most of the larger tablets like the Dell XPS 18 and Sony Tap 20 because they have capacitive digitizers instead of active ones. (Capacitive won't support pressure sensitivity).
The thing is though after a while of searching for info on tablets that did have active digitizers, none of that can guarantee that the drivers will be supported by ZBrush or Photoshop!
So after reading a really good thread over on ZBrush central (here), I'm convinced that unless you have $2K to spend on a Lenovo, that the Surface Pro is the way to go.
Here is my main reason: Community Support. There are a lot of ZBrush artists using a Surface Pro. It was evident from the fact that initially there was no support for pressure sensitivity in ZBrush to having full support a few months later that Microsoft/Wacom wants the Surface Pro to succeed for artists and is putting good work into driver support. If there are problems, the community will shout and it looks like they will be heard. Probably not so much luck on a less popular tablet.
Also, if you are having a problem, chances are that many others are as well and have found a solution. Like the Art Dock software that adds button support (like Shift, Alt, Ctrl etc.) for art programs. Though I understand that it works on many other tablets as well.
It has now been tried and proven to be a success. Just watch this video: