I would have to measure it again, but I remember seeing numbers much higher than 4% peak when I had to use Office. It could be some other latency disguising as CPU usage. The fact is it's been a while since I last used Windows and Office 2010 and I would prefer it to remain that way.
Also, consider that A-15 may be competitive with current x86 designs. Who knows what will Intel and AMD bring by the time A-15/Denver machines hits the shelves.
That said, I find my modest Atom good enough for Django programming the slightly less modest Core i5 very reasonable with Java and Eclipse. It will take some iterations until ARM catches up (I assume it will move faster than x86 because of its simple architecture). I have no doubt a relatively modest ARM machine will be good enough for most of my then current usage.