Typing in the storm cellar with the lightening diverter's activated, I have used both as a veterinary technician, Thorazine works on smooth muscle and brain, i.e., we used to give it to dogs that were vomiting to stop it. Having used both on cattle, ace will drop a top in a minute and just flat knock them out if you use too much, Thorazine works a little better for just taking an edge off.
That being said, if the calf is already "excited" when you give it to them you have a strong chance of making them flat out crazy and getting them even more wound up.
I would use a tube of calf calm 4 hours before the show, if you don't notice an improvement, hit it with another one in a couple of hours. It is legal and if the calf is that goofy maybe you don't want to be showing it anyway and taking a chance with it. I personally know someone who gave 3 times the dose and it didn't hurt the calf at all and worked perfectly.