upgrade.
when I was a 5 I never finished in the top 10
IMO, category purpose (very loosely put):
cat 5 is to get so that you can ride in a group without ****zing out
cat 4 is to learn how to get yourself into the top 6 (USAC upgrade points - that has changed, but generally still applicable)
cat 3 is to begin recognizing/implementing strategies and team tactics, how to race as a team member, how to race against others doing same, get individual results and assist others in getting results
cat 2 - I'll let you know in July
masters - where cat 1s and 2s sandbag for extra walkaround money