I haven't thrown these particular cover/cover matchups, but I'm familiar with the traits of the cores and covers from them.  In my opinion, there won't be much overlap here really.  The R2S solid coverstock is a good bit stronger than the Reactor pearl, so the Rapid Fire is going to handle a lot more oil than the Agent will (especially if you knock the polish off it).  And actually, if you drill them right, you might actually end up getting somewhat similar types of motions on different volumes of oil.

It's "stronger," yes, but it's not like we're talking about the Agent core versus a 3 piece pancake weight block or something.  The cover is much more important than the core in determing overall ball motion.  The diff on the Fire line core isn't low enough to make a huge difference, you're getting just into the RG being higher than the Agent core which encourages cleaner motion through the fronts and a slower transition into the hook phase.  The much stronger R2S solid coverstock will still give you a lot more traction in oil than the weaker previous-generation Reactor pearl.

I have both balls drilled the same.  The solid for me is a bit earlier and smoother.  The agent is a little longer and stronger in the backend.  The agent is  more flippy.  I think both balls compliment each other very well.  If I could find some more agents new at a reasonable price I would quickly get them.