Everyone is bringing valid points. I would say something that can be taken away from this discussion is that western grips allow for stronger rally balls, but weaker "rips" or smashes. Although, I could still be wrong
I would think that someone with an eastern forehand could smack a flat shot harder and faster, but it would be lower percentage.
Usually I swing at similar speeds for my rally balls (or slightly offensive balls) as my rips, but my rips are much flatter shots. The rips are more of a line drive with topspin to bring it down, while my rally shots have somewhat of a quick arc up and down. I do hit loopier ones on the extreme defense or when I feel like being mixing it up (or the occasional *cough* mistake *cough*). I don't often tense up and just smack the crap out of it, but that is probably just my style of hitting.
A rally ball can be kind of a hard term to classify. A lot of times rally shots are not exactly even, but are at least close. One player could have a slightly more offensive rally ball