I'm in this exact situation (will be purchasing an IRO, but which one??) so I'll weigh in and pose a question or two to the smart kids on here

The BB drop is something worth looking into.

The Jamie Roy has a 7cm BB drop, meaning that the pedals are closer to the ground than the Mark V (5cm BB drop). This seems to be a concern among some riders here, because you obviously won't be able to coast thru the corners and could possibly clip the ground with the pedal. I don't have any experience and wonder what size cranks those out there run with the Jamie Roy successfully.

The Jamie Roy is aluminum. Supposively that's a much harsher ride than the steel bikes.

The Jamie Roy is more road-bikeish in geometry.

I'm sure some Jamie Roy owners will chime in, and Mark V ones too.