based on the flyer, the Cat 5 is a seperate race from Cat 4, starting 5 minutes behind the 4's.
In all likelyhood, the 5 pack will stay behind the 4's and you won't have issues. If you do find yourself with racers from other Cats (which should only happen if your off the front or off the back) remember you can't legally work with them
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.