Is it possible to optimize server requests to fit the circumstances?

I love to optimize my codes, regardless of language. Is there a way to adapt requests and load on screen to fit the users bandwidth, platform and other circumstances to make the system 100% responsive?

Lets say I want to get a long list in XML from a database somewhere that will be shown to the user. I am using an old PC that would require a long time to load the entire list and instead, I want it to load asynchronously while I watch the data that has managed to load. Is this possible with web programming today?