The JPop was removed in the US releases of X4, and the English voices aren't exactly great. I'm noticing a ton of little details that seem better in the original, like the "Ready!" voice. I'm not sure why something like that was redubbed, since it's in English to begin with! The localization of X4 never struck me as amazing, so playing the original is just something I've always wanted to do.
I have the US PC version of X3, which is a port of the Saturn/PSX versions. Sound effects and overall audio seem better on the Saturn version, and the JPop is intact. There's also sidebars that change from level to level, possibly to compensate for a different pixel aspect ratio (?), while the PC version went fullscreen just fine.
Super Adventure Rockman was never released outside Japan.