OP, if I were fortunate to have the option, I'd race the Masters 4/5. Better bike handlers, less suicidal. Unfortunately, over here there are no categories other than age with regard to masters racing, so I either race against everyone in my age group, or everyone who is a Cat4, regardless of age.
I do the latter. The Masters races invariably find people like me lining up against elite cyclists and the odd ex-pro. Way out of my league. So I settle for the Cat4 and get beaten by the kids, but not so badly.