I'm not sure I'm getting the whole purpose of this thread.
If your MBA experience really gets you 10-12 hours of full time Office (Word, Excel, etc.) use on a single charge, and you need that capability, then the Surface Pro 3 is not for you. Any reasonable usage (beyond low light, low usage browsing) will get you 6-7 hours tops on the SPro 3. Personally, my daughter has been using MacBooks (latest is June 2013 Haswell) since starting college through her current doctoral program, and although it has excellent sleep/resume ability, she has never gotten 10 hours of real usage out of it - more like 8 hours tops of writing papers and researching on the internet while on battery - WHICH IS VERY IMPRESSIVE TO ME. Still, that entails a lower resolution screen (1440x900), 30% screen brightness, and the larger battery that a MBA contains. If handwritten notes are not your "be all, end all" use for your computer, then I'd stay in the Apple camp to maximize time away from the outlet.
Now the decision is in your hands...