How fast will a web app load

I am concerned that the web app I am writing will have a ton of latency issues. Obviously when the app is run locally it loads briskly, but I am concerned that once deployed that it will take forever to load for people with a slow connection. Is there a way to simulate a deployed web app to gauge how fast it loads and operates?

If you have a Mac, do a google search for Network Link Conditioner. Its a preference pane which allows you to simulate network issues, including latency issues.