Welcome Celtricfrost. Cat 5 races are for beginners to learn how to race in larger fields. It is not about placement. Downgrading to a Cat 5 from a Cat 4 will probably not be understood / allowed by USAC with the primary reason being to circumvent buying a USAC yearly license as a Cat 4. But hey, give them a call. Maybe it will work.

As a side note...Depending on how old you are...there is an advantage to being a Cat4. Cat 5 racers are usually excluded from masters races. You may find that you like racing and want to compete in a particular masters field and cannot do it as a Cat 5.

Raw power is an interesting concept. I have found that generally it works for those times where strength is a competitive advantage such as sprinting or gaining separation in the first 4 pedal strokes. For me, the better weight management I maintain, the better my longer term power - both flat and hillclimb - YMMV.

IMO, weight management is the trifecta of endurance cycling...Lower CdA (smaller frontal area i.e. smaller body), better internal heat management and improved power to weight ratio.