I should have specified I was considering the Pletscher Orion (though people who have used the suspension pannier rack claim it does actually work...) I'm not sure I need panniers on the back - R&M themselves recommend carrying most of the weight on the front, and also I don't know if rear panniers would fit with my big feet

I hadn't actually considered mounting the Pletscher suspension rack to the Birdy mounting point... hmm, that's an interesting idea. I'd have to say I think the suspension rack looks a bit.. <cough> dorky.. but maybe the ability to fit panniers, should I have to, is worth it?