Is this really true? I have read this here several times but I have been told by reputable shop owners, manufacturers reps, and a manufacturer that it is not true.
It is true, as I have observed from experience. The T. Rice has better float in pow than a cambered deck of the same size. The T. Rice is made for long aggressive carves and big booters... I'm not sure what you mean by over carving... The Magnatraction definitely makes the carve want to stick more, but as long as you are going fast, you just lean onto the other edge and carry the carve around in another direction...
That being said, I can take my T. Rice 161.5 HP in the bumps all day and feel fine with it... In my case, and from what else I've heard the 161.5 has 180 lb riders on it.. give or take 20 lbs... Your size (the OP) seems perfect for the smaller deck, as a longer one would just hold an edge better and be harder to turn.