I've had my boat out three times now since I got my rack so I thought I would chime in here. First off, see the pic below showing how I have mine mounted. It's a double clamp and I have the rack slid forward as far as it will go. I had my 5'-3" CWB Ride on it today, upside down with the nose of the board pointing towards the back. When pulling a wakeboarder, the rope goes just over the top of the nose of the board when the boarder cuts way wide to port. So it's not an issue for me.

As far as double versus single clamp, the double clamp will obviously be more stable as it will not be prone to rotate like a single clamp might. However, as you can see in the pic below, if I had a single clamp, I could mount it to the front tube and that would move the rack about 4" forward from where it sits now. That should be enough that the rope would not hit the board when a wakeboarder cuts out wide. I could easily drill a hole in the center of the rack and convert mine to a single if I want. So for the same price, I guess I would get a double and then just drill the hole and convert it to a single if you need to.

Note that the clamps I am using are not the ones that come with the rack - they are from a set of Fusion speaker cans.