Candi Murray

You can only ride in a field that lists the category you are on your
membership card. Not in any race, not PIR, not any race.
If you are a Cat 5 you cannot ride in a Cat 3/4 race.
This means that if you are a Cat 4 you cannot ride in a 1/2/3 field. NEVER.
If you want to ride in those fields then upgrade like everyone else. The
upgrade guidelines are on the web at http://www.obra.org/upgrade_rules.html