I really hate preparing for tech talks, when they are formal and far in advance. I have too much time to think about it, tweak it, etc, and I slowly go crazy.
I have one coming up in 5 weeks, and I'm starting to dread the 'end game' where I wind myself up for it. It's pretty much all I think about, and I have a lot of other stuff to think about.
I'm much better in a spontaneous setting. Multiple people have called me a professor because I can summarize a topic in 10-15 minutes fairly well: just give me a whiteboard and let me go.