I've said it for years. I just stated the port floor differences in another thread yesterday or so.
X head has a flatter ssr peak. You can about wipe the turn flat before you hit water too in an x head. But the real deal is if you know how to port a j head...it flows better than an x head .100-.450 the turn doesn't need to be laid down as much. To each his own.
I can only speak from my experience.
I have no reason to believe this statement is not totally accurate. And goes along with what I've read over the years. But stock to stock I don't think you could tell the difference by the seat of your pants
