Originally Posted by
vendsit
The train is 6 hours and I don't want to waste a good portion of a day on it.
The high-speed train is 3:50 hours (from Amsterdam Centraal to Frankfurt Central Station) or 3:35 hours (from Amsterdam Central to FRA airport). It runs every two hours.
From door to door, the train is going to be almost as fast as a flight AMS-FRA. (Assuming that you're staying close to the central railway station both in Amsterdam as well as in Frankfurt which makes sense as a tourist.)