I'm not sure the Surface Pro line is really competing with the iPad, though. I mean, according to Microsoft themselves, a Surface Pro 3 is equivalent to a MacBook Air.
(Disclaimer: I own a Surface Pro 3. They're probably right to compare it to the MacBook Air and not the iPad. I know everyone hates the "tablet UI" on the desktop but even with the Surface Pro 3 their tablet UI is still pretty terrible. I pretty much never leave the desktop. On my tablet. The few tablet-style apps I've tried for the Surface has all been terrible. It really does make a descent small Windows laptop, though!)