I'm looking into assembling another Remington 700 to use for varmit hunting. I'm looking at .220 Swift or .204 Ruger, both of which travel 3500-4000+ fps depending on bullet weight. I know very little about suppressors but if I understand what I've read, the best performance in terms of noise reduction is achieved with a subsonic velocity. That could be a 75% reduction in velocity for these calibers. Is that even possible? I would be shooting inside of 300 yards at coyotes, bobcats, or foxes. Is it even worth putting a suppressor on a bolt gun like this?

Looking for some knowledge here from those of you that know more about this than I do.

Many thanks.

I wouldn't hunt with subsonic loads unless you are really close. The suppressor will make your shots hearing safe. It's like a muffler. You are still going to have plenty of noise but it's much better. You also get recoil reduction with a suppressor so it may help on follow up shots if needed.

It will make everything about shooting more pleasant on your end.

Shoot supers.

Suppressed is still plenty quiet with supers. And, if you have any kind of backdrop behind the animal (tree line) they have trouble locating you. Hogs, and deer have come toward me, after I hit another one in their sounder/herd. Cycle, shoot another one.

^^Doing this makes work, and you'd better have sharp knives.

I have some info on this in my Ammo 101 page on my website. Your 220 Swift or 204 would not make for a good sub round, due to the low twist rate.

https://dallasreloads.com/2018/06/26/what-is-subsonic-ammunition-and-shooting-with-suppressor/

Hell yes it is worth it. Even with supers you just hear the crack going over sound barrier and it is not bad at all in most cases.

I run a can on my 22 creed it's not exactly as fast running a 90 at 3350 but it's extremely loud with the amount of powder vs bore diameter. With a can it's so much better to shoot.

do a can
be happy

If possible, I’ll never hunt/shoot without a can

YEP!
I built a very lightweight 7 mag recently and my 6" Crux Nemesis 30 cuts the recoil down to like an unsupressed 243 with no muzzle blast

I still shoot supersonic through my rifle cans unless I'm using my 9mm carbine for pigs or whatever. They are still plenty quiet.