I've always wondered why people say 25%, when the tooltip says 20%, is the tooltip incorrect? Though I have seen on some sites that it says 25%, but not entirely sure.
I don't think it's quite fair comparing Rampart to IB/Storm's Path mostly because you aren't going to use the ability guaranteed as soon as it comes off CD, while there is no reason not to use IB/Storm's Path whenever available. That and it's use will not differ from fight to fight, while things like Block/Parry will depending on what abilities the mob uses.