Hoo boy do you have an exaggerated notion of how fast you have to be to be competitive in Cat 5. Averaging 22 mph solo is not easy to do, probably threshold or somewhat over for me, and I'm a regular Cat 4 (so, still slow, but a bit better than Cat 5). 25 mph? That's VERY fast to ride solo for an extended period of time.

Obviously you need to be faster to do well in races, but you don't need to get crazy-fast. Mostly you need to be able to respond to changes in pace and recover from anaerobic efforts. Only one way to find out your weaknesses - race.