For the blue and white NFAA 5 spot round a perfect score is a 60X 300. Each arrow is worth a maximum of 5 points and 5 arrows are shot per end, 12 ends total. The X is a smaller circle within the 5 ring that is used to break ties. Most tourneys with better shooters, the majority of people shoot a 300 and then their X count is used to determine their place.
The X ring on the 5 spot is the same size as a 10 ring on the vegas target (which has an even smaller x ring slightly larger than a dime). The Vegas target is a more challenging face that further rewards shooters for accuracy with its smaller X ring. When you see 20 something "X's"/ 300 game, they are generally talking about a vegas round.