I can't compare them yet, though I have a new McCarty, and a 594 on order. However, the McCarty video on the PRS site sounds just like my McCarty, and I'd bet for that reason that the 594 video sounds very much like the 594.
You've probably already heard both videos, but if not, that'd be a good place to begin, because the two guitars do sound different in the videos.
I do have a McCarty Singlecut, a PS version of the Singlecut, with low turn 57/08 pickups, the flatter frets, the bone nut, and the two piece bridge that the 594 has. These things all make a noticeable difference in the tone of the guitar, and it does sound different from an SC245 in much the same way that the 594 sounds different in the video from the McCarty.
In other words, there's much more of a vintage LP sound.
And the 594 has the 4 knob layout that lets you blend the pickups, including their relative volumes and tones. So there's a world of exploration to be had that the McCarty can't do.
OTOH, the McCarty is a fantastic workhorse of a guitar, and I love mine.