Horton's reviews of each might help:
http://www.ballofspray.com/home-v16/2011-ski-tests/2011-ski-tests/996-ho-a2-review
http://www.ballofspray.com/forum#/discussion/5141/2012-radar-vice-review
I'd try deeper in the finger to start. Overall looks better protected. And you can always move the course if it doesn't work out. Have you run both those proposed paths to see if either might give you some unanticipated rollers coming back off the shoreline?
The Mid S was designed more as a fun freeriding ski. It might carve a decent turn but wake crossings in the course could be an adventure. 71" HO Triumph or 71" Radar P-6 might be better choices.
A little more expensive but you don't have to find a core to fit your box, and drill the rivets out of your existing box.
http://www.skidim.com/products.asp?dept=1020
If the screw fits tight in the hole, you can apply a layer to the amount of threads that'll be in the ski and install wet. If the holes are a little big, fill the holes, let it cure, drill a pilot hole, then install the screws.
It's easiest if this is your first time doing it to remove the rear boor or toe piece and measure from the back of the heel rubber on front boot to tail of ski (down the centerline of the ski). If your screwing your front boot to the ski using the holes in the enzo boot plate, pick the set of holes that gets you closest to 29.625".
I'm very happy with my Senate (non C) in and out of the course at 34mph. With that said, you probably can't go wrong with either ski. Both will be forgiving in the open water and still will allow you to progress in the course. If you have a chance to ski each, go with the one you feel more comfortable on.