I've done 5 Tough Guys all from front squad both in a short leg wetsuit and normal running gear, one year of madness in a thong. I can tell you what makes all the difference is some kind of thermal headwear.Either a neoprene cap or a couple of layers of swimming caps. Also neoprene gloves to both keep the hand warm ad for protection.
The cold is easy to deal with, but putting your unprotected head multiple times under freezing cold water makes you feel like you have been hit in the head with a shovel.
If you're thinking of wearing a full wetsuit, and think you can run a couple of miles in it I say go for it. Just make sure no one can see it or you'll be abused for however long it takes to get around.
There are loads of other entry routes still open after the general ballot date ,which is why it takes so long to decide how many places they give to the general ballot. Deffered entires, good for age, oversea entries. Deffered entries for examples don't have to be for at least another month. Good for age is even longer, sometime in July.