I wouldn't remove stories from a sprint but I would make sure the product owner has them prioritised. That was, so long as they are informed how far over you're likely to go, they'll have a good idea how far through the sprint commitment you'll get.

Equally, if you're getting through stuff quicker, make sure the product backlog is well prioritised and you can pull in stories from there if you get through your commitment.

The key for me is communication with the product owner so they don't get any nasty surprises.

You might want to try shortening your iteration length. The shorter the iteration, the less variation you're likely to have.

I wouldn't remove stories from a sprint but I would make sure the product owner has them prioritised. That way, so long as they are informed how far over you're likely to go, they'll have a good idea how far through the sprint commitment you'll get.

Equally, if you're getting through stuff quicker, make sure the product backlog is well prioritised and you can pull in stories from there if you get through your commitment.

The key for me is communication with the product owner so they don't get any nasty surprises.

You might want to try shortening your iteration length. The shorter the iteration, the less variation you're likely to have.