Don't rush yourself into a decision on what gun to buy. You don't need to take that gun to the class. Renting one of their guns might not be a bad idea for you.
The course will teach you tactics and techniques that can be used with just about ANY pistol. You don't need to re-take your drivers liscense test just because you buy a different car, your skill set remains the same. And it doesn't really matter much what kind of gun you take to the class, provided it functions properly and you like it.
Having said that, if Front Sight kept stats (they probably do) on which guns people use in that class, you'd see that VERY few people have ever brought a 5.7 to use. There's a reason most people shoot Glock, XD, 1911, Sig, S&W, etc in basic calibers. Call them and ask what they recommend, you'll see.