Actually, it's not that different (to talking to 20 people). You'll probably be interrupted less often and it may be harder to make eye contact with people, bu

Actually, it's not that different (to talking to 20 people). You'll probably be interrupted less often and it may be harder to make eye contact with people, but if you've already given talks then you're way more than half way there. So instead of being worried, think of it as a chance to give a really excellent talk where you're going to be able to say what you want with less interruptions. Go for it (and good luck :o)