(1). Apparently, speed is at least partially related to age and size. Later in life, Balerion was considered slow. When Aemon, Alyssa and Baelon used to race back and forth between KL and Dragonstone it was usually Alyssa and Melys who were fastest.
The fight between Tessarion and Seasmoke was considered the fight, "where the dragons truly danced."
Now whether this also applies to how far a dragon can fly is another matter. Unlike, the speed issue we have no direct textual evidence. My best guest would be that the older dragons can fly farther at a slower pace. Balerion somehow made it to Valyria and back without being noticed. That would imply that he spent a large portion of the trip either flying over open water or otherwise avoiding populated areas.
A good comparison might be a Tesla and a tractor-trailer. The Tesla is fast and agile, but has a relatively short range. The big rig is much slower and far less agile but can travel much further without refueling.
Then again, we're dealing with a magical world, so who knows.