How many times can you present the same material at different conferences before it becomes stale? I just finished my PhD in Mathematics and am in between my PhD and postdoc positions.  I was very fortunate to have the ability to present my research to seminars and conferences over the last couple of years. My complete results all reduce to a standard storyline and I feel like I have spoken about it to various audiences a lot, especially the specialists in my field. I have a conference coming up with the specialists again and I am a bit concerned about giving a talk that is just a minor mutation from the talks before.

My question is therefore: 


How long can one talk about the same material in the conference loop until the talk becomes stale?
Is a repertoire of multiple research talks expected of a recent PhD?
It's important also to look at your audience. If you're likely to be giving the same talk to two audiences that overlap significantly, then the time between talks is less important than the fact that the audiences will perceive the talk as 'stale'. 

For example, you might give a talk at a general interest conference, and then a slightly modified version of it at a workshop with specialists, many of whom may not have attended the general interest conference. That would be fine. You might then go on the colloquium circuit and give the talk at venues with only small overlap with the specialist group. 

But if you gave the same (or similar) talk to the same (or similar) audience more than once, that would be a problem.