I'm new to serious biking, but not to serious exercise. I agree with Irulan about listening to your body. As long as you're not experiencing the symptoms of overtraining, it sounds like you are working with your capacity. But, variety is a great thing, so if you like to work hard, maybe you could vary the WAY you get the intensity. (I always scoffed at low-weight, s-l-o-w weight training, until I tried it and realized that it is extremely intense and challenging, but in a different way.)