I never dove the Channel Islands in March but have many times the first week of October. 7MM wetsuit, no hood and just non insulated gloves for bug diving. My guess is that the water should be closer to 60 -65. As mentioned, everyone's tolerance to cold is different, and I happen to have a nice extra layer of some built-in fat to keep me warm. Up here in the PacNW the temps are pretty much 48-52 all year. I dive a Scubapro Tri Lam and use a basic rashguard as a base along with a Lavacore front zip that's basically a 2ml with fleece for warmth. Low profile, low bulk and also serves as great warm water exposure suit..
I should also add that earlier this year I did by the two piece 4th Element Artic undergarment set from Liesurepro (Scuba.com) and for me the set turned out to be too bulky and too warm so I returned it..... Gotta love the scuba.com return policy!