I recently bought a Surface Pro 3 for the exact same reasons you mentioned. I had taken some videos to put together for a review, but I haven't sat down to make the movie yet, so here's some textual context.
The Surface Pro 3 is a great device. If only the software on it were more specialized toward making art, it might have been a viable option. For me, I decided it wasn't. Most of the reasoning behind this for me was the fact that I was never sure what mode I should be in: Metro (tiled interface + apps) or desktop. I loaded Photoshop CS5 on the thing in desktop mode and the interface was infinitesimally small. Added on top of that, the pen didn't seem to recognize strokes very well in that program. Things fared much better in Manga Studio 5 and the preinstalled One Note application, but I didn't want to use a note-taking application for drawing comics on the go, and I foresaw frustration with Manga Studio simply because there's no good way to do shortcuts. I use an Intuos Pro at work and an Intuos 4 at home, and I'm dependent upon having some controls for my brush size, canvas zoom, eraser, undo, redo, etc. If I were holding the Surface Pro like a tablet (probably in the crook of my arm), the only way to accomplish these was through the menu. Perhaps there might have been a third party toolbar application I could have installed and configured, but I still thought it would be frustrating to have to dip and roll the pen over the screen just to get the tool I wanted. I'm a keyboard addict, plain and simple.
Then there's the fact that even though Windows 8 is a pretty good operating system, I just prefer OS X. I'm too used to the keyboard shortcut system, and I just don't have the patience to deal with Microsoft's more cursor- and menu-based operating system.
Edit: forgot to mention, the pen and digitizer are fine. I've used Wacoms all my life and I didn't feel let down by the N-Trig at all. Palm rejection is top-notch, too. The touch keyboard is a required accessory, and much improved over the previous versions, especially the track pad. The thing felt damn speedy to me, although I wasn't using very super-intensive programs on it. The Wi Fi seemed to buckle a bit under intense load. It's nice and light, much more than you'd expect, but it's not iPad Mini-light.
So here's what I'm gonna do. I returned the Surface Pro 3 tonight (BB). I ordered an Intuos Small (the new name for the Bamboo tablets) off Amazon last night, and am going to test that with my current Macbook. Provided I'm happy with that as a mobile studio, I'm thinking I'll probably (finally) upgrade to a new 13" rMBP. The 2007 dinosaur I'm currently doesn't even get 2 hours of battery life, and this is the third battery I've been through. If not for that, I'd probably keep using the damn thing. Expresscard SSDs and 4Gb of RAM can keep you going for a pretty long time.
My recommendation for you: get the device that's more comfortable for you. If you're a point-and-click type of guy, the SP3 might do fine for you. If you're a Mac enthusiast (and it sounds like you are), it might pay to stay in the Apple walled garden. Plus, what with buying a laptop and a separate Wacom, you can decide whether to bring one device or the other depending on your needs for the day. And they're both good at what they do.
A third option would be to buy a Wacom Companion Hybrid, however, I've heard the battery life on those is not great, and you'd be dealing with Android drawing apps when you're on the go. Not necessarily a bad thing, but just something to keep in mind.
