If they said it's rated to 52 they are being conservative. I have a delta3 and a GT3 and have had both in 39 degree water in Lake Erie with no problems on more than one occaision. One of the factors in reg freeze up is overbreathing the reg. Keep your breathing nice and smooth and slow and for the most part any enviro sealed reg will do fine. Get a GT3 with the cdx5 first stage non dvt. Will save you alot of cash and be good for most anything you do. THere are techniques for ice diving that would be discussed in the course to also minimize reg freeze up in and out of the water. As to your other choices the Excursion is a nice unit and personally I'd go for a standard octo based on experience with air shares and the type of diving you plan to do.