You seem to believe that ARM performs quite poorly compared to x86 (assuming similar clock speeds). Could you explain why?

It seems like if something could run on a ~166 MHz Pentium, it shouldn't be a surprise that a Tegra 3 (probably 1.5 Ghz or more) can run something similar. And older versions of Office ran on much less.

Even then, Apple put Pages on the iPad 3 years ago, so that should prove word processor like software could run acceptably on an ARM. The Surface is clearly much more powerful than an iPad 1.