It's become an ancient canard that #1 buckshot in a 12 bore has some kind of huge theoretical advantage over any other buckshot size, since a load of #1 can hold more pellets of a useful size. Unfortunately in my long experience (I was first informed of this theoretical advantage in a hunter safety course in high school in the early 1970s), reality has always trumped theory. In other words, having more usefully sized pellets in a load of buckshot is no real advantage IF THEY WON'T PATTERN WORTH A DARN. And I have yet to own a shotgun barrel that will pattern #1 better than it patterns 00.
IIRC the article on #1 buck being the ne plus ultra of defensive shotgun ammunition is at
http://www.firearmstactical.com/briefs10.htm . If that's so, why do so many law enforcement agencies still issue 00 (not to mention the US military)?
So it's still 00 for me, thanks. Of course, if someone would just make #1 sized buckshot in Hevishot, and then load it in a FliteControl wad, we might REALLY have something there.
As to the #4 buck issue, it'll probably do as long as you can get it on target. But in a world full of options, I'll stick to 00.
Stay Safe,