Most ATI/AMD problems are caused by old drivers. We did not yet find a direct issue with the newest driver and an ATI/AMD card that’s supported. We are testing with several ATI cards in our office.
On the steam forums there was once someone who had a problem with his sound-system driver causing low fps. It could be any other software/driver that’s interfering with Train Fever.
As you guessed right, Train Fever should run without any problem on your rig. We don’t address this as done, but unfortunately we can’t focus our resources on a particular system setup with fps issues. If the next release note contains performance changes and you’re still having low fps, we would appreciate when you’re still keeping us informed about your problem.