Re: 204 Ruger
This is one of those theoretical discusions, on paper. A 220 Swift and a 204 Ruger are so different that you cannot crunch those numbers and prove your point. There is nothing new, under the sun. In this case, bigger is better, in every measurable aspect of performance. Terminally speaking.
You have wind to consider; and the various presentations. A 220 Swift is not a squirrel cartridge, and the Ruger (actually) is neither fish nor fowl. For me, at least, it is hard to define. I don't see it as a serious chambering for large predators; and this is where the Swift excells.
So, if it drops an inch more, or an inch less at 500 yards, that doesn't begin to tell the whole story. The original question mentions that the man is interested in a 22-250 or a 220 Swift, but the 204 "looks good, on paper".
That's about the only place it will compare to a Swift, IMHO.
Good hunting. LB