I have the combyn and I/O7, haven't used them together yet though. I know the I/O7's are a bit more of a rounded goggle, especially on the sides, and the combyn is pretty straight across in the front (it fits perfectly with the Giro Axis, which has a fairly flat top edge).
Not sure when you're trying to pull the trigger, but I'll be able to give a better description next week when I have access to them, but hopefully someone else can chime in beforehand.