phatkid77...
I've found that in order to hold on to my mass, I can't ride as much as I used to-when I was 16-18 years old, I was quite a bit smaller (obviously) and rode usually 4 days per week for 3-4 hours at a time. These days due to a change in physical goals, I limit long rides to once or twice per week (or even every two weeks) at most. Short rides 20-25 miles are no big deal, that's only an hour or so of cardio for a cyclist in decent shape.
I put a focus on two things- 1: making sure I have a steady supply of carbs in me during the ride so as to spare muscle as much as possible, and 2: making sure that my post-ride routine includes a lot of food and a ton of sleep. The addition of BCAAs to a water bottle during a ride is probably not a bad idea either.
I too am preparing for a show next year, and I will use my bikes as a source of cardio. Since you ride a road bike, let me mention this-road riding is a great avenue to get in some interval training without the outrageous pounding on you that sprinting (running) will produce. I can go out for even just a half hour hill workout that will put to shame anything I could do for cardio in a gym setting. As far as your back-to-back century rides go, I don't think it will really be a problem as long as you don't do it week after week. Just make sure you put a huge emphasis on recovery, just as I'm sure you do every time you hit the gym.
A side note for you guys with tiny calves...this is what cycling can do for you (I haven't trained my calves in the gym in years):