Originally Posted by
superdex
5. It will be hard enough.
Master 45+ will be 'open' which means you'll be blown off in just a few laps.
A lot of races will let you sign up for multiple, so there's no harm in doing both, though if the Master's is first you may be too toasted for another race.
In addition, one reason everyone starts as a CAT 5 is so they get some experience racing before they're thrown in with (and endanger) more experienced riders.