I'm with Ex on all fronts. Race both Cat4 and Masters when you can. Race Cat4 for the win and use Masters for training. The Cat4s are still loaded with guys who race like Cat5s so they will chase pretty much everything, however the Masters will not. Use the Masters to try stuff like bridging to a break or soloing for a prime. Finally, don't lose perspective just because you upgraded to Cat4. You are still a beginning racer even without the 5 on your license. Watch, listen to your body, try stuff, and don't be afraid to lose.