Tough to answer without knowing if you've used steriods before, or what kind of workout routine you have. If you've never had a solid rotator cuff program, then perhaps you should look into your training routine before considering roids. That being said, I think test prop is a good choice. You mentioned equipoise and that is something I like too. As a side effect EQ is said to increase collegen synthesis in connective tissue and that's always a welcome thing for a pitcher.

As far as your expectations for 5 mph, XXX is right, you can't just added velo like that. Read my earlier posts where I stress a solid rotator cuff program. You might have a couple MPH in you right now that your not using because of a cuff that's not conditioned well enough. Remember, pitching is very harsh on the shoulder, it gets pretty beat up, even early in the season. When you condition those decelerators properly, you'll find your arm strength will definitely increase. But you won't be "adding" mph, you'll be tapping into your natural potential.

Obviously getting stronger all around: your trunk, legs, etc. can make you a better conditioned athlete and better equipped to handle the physical stress of pitching. As far as I'm concerned all weight training that a pitcher does should be done with the purpose of lending support to your shoulder/arm. Think about Roger Clemens. As big and conditioned as he is, he doesn't have nearly the kind of stuff he had when he was a skinny 25 year old. All that mass and strength he has now, he put on help handle the stress and keep him out there into his forties.