Salsa,

I think you need both long road rides (to build endurance) and at least one longer off-road ride (to build confidence, knowing you CAN do it.) What I've read (and experienced) is that you can do AT LEAST 25% more mileage in a competive event than you've trained. Your adrenaline and competitive spirit kicks in and BOOM! You just get out there and GO! Do some long road rides. Do some tough miles off-road. You'll be ready to jump into the Sport Category. Have fun!

Annie