444:
I have direct experience with subsonic 36gr and 40gr 22lr, and direct experience with subsonic 45, 50, and 55gr .223.
BY FAR, the best of the lot is the 55gr .223 going ~975FPS, in terms of downrange impact on cute little squirrels.
My favorite load is
3.1gr of Clays with a 55gr Combined Technology ballistic tip "varmint bullet" going about 975FPS...
may or may not be safe in your guns, not my problem if it isn't.
BUT, yes, it's slightly louder through my AR-15 and PLR-16 with an M4-1000 ('08 manufacture) than .22lr through a 10/22 with a TAC-63 (with -65 baffles).