The Cat 5 rating is usually used for trailer yacht racing in protected and sheltered waters when there are no rescue boats on the race course.
If your club has a rescue boat available then they are allowed to declare it a Cat 6 race which will reduce your safety equipment costs. I found it quite confusing complying with all the State boating and the YA rule book requirements. The boat I race at the moment is kitted out to Cat 5 N which covers me for night racing here on the Gippsland Lakes and this is also the minimum safety level for the Marley Point race.
Have a look at the Special Regulations section in the current YA Rule book (page 183). If you do not have a rule book you can have a look in Yachting Victoria’s website (click on Safety then Safety Declaration forms) but I do suggest you just use the rule book to reduce any confusion.
Cat 7 is ok for the racing I will be doing initially. My boat is cat 7 compliant plus some, but I don't have a locking device for my keel, which is required for cat 5/6. I guess cat 5 is reasonable for an RL24. My club requires lifelines for cat 5 so I have a little bit of work to do to make it compliant.