How are those 60gr SP's performing? We've got those loaded in the .223, but haven't shot a coyote with them yet (although we'd have to compare your 400 yard shots to our 4 yard shots for similar velocity - lol)
Assuming pelt damage isn't a big concern, bullets don't matter nearly as much as bullet placement. I've had great results with .17 Rem 25gr factory, both 35gr and 40gr. Bergers in a .204 and everything from 45-55 gr. in a fairly long list of .22 CF's. That said, I prefer HP and PSP and am not a fan of plastic tipped bullets on anything but broadside shots. I've probably used the .22-250 with 52gr sierra BTHP's for more coyotes that any other single bullet, and have been very pleased with their lethality and still being easy on hides. I haven't shot anything heavier than 55gr. in .22 cal yet, but have ruined a few pelts with the old Speer 75gr, HP's in a .243 (huge HP and gruesome effectiveness) as well as a handful of incidentals with 7mm-08 and .308 while chasing venison.