You're right, I've never seen anyone using a 45 for hypers. I did a 5x5 routine a while back wherein the last exercise each day (crunch variations, hyper-extensions, and rotator-cuff work) was 3x15 because the goal for those specific exercises wasn't so much to build muscle or max. strength, but to increase endurance and agility and minimize the risk of injury. That being said, if 3x15 with a 25 isn't doing it for you, move up to the 35, just be careful.
