First five pages

Send five, as that's what they asked for. They assume it won't be a complete chapter. And if they like it after five pages, they'll want to see more. If they don't like it after five pages, the next page and half won't make a difference.

The pages are just a way of checking quickly if an interesting query is worth asking for more of not. They don't read all five pages for every query they get.

I agree with Danthia. Follow the agent's guidelines. If they said send five pages, then send five pages. Always follow the agent's guidelines is a good rule of thumb.

Send the first five only. That's plenty for them to make a judgment. It also shows you are professional --- you follow instructions!