I apologize that you had to hear the guitar via my lame demo! I'm a little embarrassed by the playing, it's way off, not that I've ever been a great player, but at least my timings weren't off before (no doubt you read my excuse, equally lame, but true nonetheless).
I have a McCarty with maple neck and 58/15s, and of course the 20th model, but I haven't played a Collection IX guitar. They both have the Gen III PS tremolo, something I think makes a definite difference in the sustain of the guitars, so that's a wash.
The Collection model certainly has gorgeous inlays unique to that line. Both guitars have similar body thickness, with slight differences in the proportion of maple to mahogany, and maybe a 1/16 inch in overall thickness, I'm not sure.
But if the inlays on the IX grab you, it certainly is understandable!
The scale lengths are different -- that may (or may not) matter depending on your needs and tastes. The feel and playability of the 24.6" scale length appeal to me, but YMMV. It's not a big difference, of course, but you can feel it.
Of course, the biggest difference between the guitars is how the pickups sound and work. The 58/15s are wonderful pickups, in fact, I cut a couple of ad tracks with my McCarty yesterday and last night. They're clear sounding, open, and do very well both clean and overdriven. I think the coil splits sound great, too. I'm really happy with those pickups and the McCarty.
The 20th PS 408s are also clear, open, great sounding pickups. Like the 58/15s, they work really well both clean and overdriven, with perhaps a bit more sparkle than the 58/15s. But the kicker is really the middle pickup, the Narrowfield, and what it brings to the party. With the 20th Anni. PS, you can pull some very nice Strat-ish sounds. The middle pickup by itself is one of the best middle pickup tones I've heard.
I also love the neck pickup tones on the 20th PS, kind of a bonus with all the other great sounds, because it's less bassy than most neck humbuckers, so you get this nice, open tone that you don't have to EQ the low end out with to make room for the bass guitar.
Though the 58/15 neck pickup isn't overly bassy either.
Anyway, both are terrific guitars, and I don't see how you could go wrong either way. If it were me, I'd base the decision on how much I would use that middle pickup, alone or in combination with the split coils of the other two pickups.
Hope this helps a little!
