In reply to Richard Carter:
On a road bike, I'd doubt it matters, and the 600s will fall into a position that's cleat side up (or near enough) once they've had a bit of run-in. On a road bike you tend to stop and start a lot less often. on an mtb, starting off a technical section without your feet in is a recipe for disaster, but on a road bike you can mange fine until you get them in (you just have less power)
Of course, this is the perfect excuse to get proper road pedals - you can get adapters for SPD shoes (or a nice shiny new pair of shoes). Proper road pedals give you a much better connection with the bike, and a better power platform. They are also one sided.