hey aabbccdd, I just took beta-blockers for the first time for a presentation myself. 20mg for me was fine, in fact I'll bet 10 would work for me. But that's because my body is very sensitive to everything (drugs). It was amazing. I still felt shy, but when I went to read my work in front of class my voice didn't shut down on me, and I didn't have to push through it, I wasn't shaking AT ALL, I did everything soooo calmly. I was so happy by it. In fact, people were laughing at the funny parts (I didn't even know they were all that funny). I have honestly never had people laughing from something I say in front of a class. It was a really good feeling. Really good. I had never been able to calmly present something before in my life.
It really really helps. It slows down your heart rate, opens everything up and relaxes all those parts of your body that try to shut down or tighten up. They say it can have bad effects on circulation and give you cold hands and feet, but I found it made my circulation better!
The only downside is it makes you very drowsy/it's difficult to concentrate. Actually I felt a little depressed (but that's probably because of the anxiety I have right now about school and life at large). And you get kind of restless. It's hard to sleep when you take them. Oh, and I am not sure, but I think it made my feet and palms sweaty a little. Could just be the weather though.
Anyway, there you go. It'll open you up a bit. The physical symptoms only though. You might still feel scared to present. You just have to remind yourself that your heart's not capable of palpitating right now. And don't do anything fast because you might feel faint (though I didn't).
But yeah, I recommend it.