They do take some time to break in and their performance will improve a lot after several days of NORMAL riding. Don't try to break them in by doing aggressive stops in the beginning, you may actually end up glazing the pads. Just ride normally. Also, you may need to re-adjust the cables after they stretch some.

Mine will lock my fat 26x2.0 wheels on dry asphalt. But on my 700c Kona Sutra they didn't seem as powerful indeed.

I suspect then that 160mm rotors may underperform on 700c wheel due to larger leverage of the wheel? Too bad most frames are no designed for larger rotors. I'm building up a Surly Disc Trucker with BB7s so I will know soon how they work on 700c wheels.

And I assume you had the road version installed on your bike? Or, if not, have linear pull levers?