60g Sierra Varmint is more of a deer bullet than a Varmint bullet. Shot out of a 1-7, 1-8, or perhaps a 1-9 twist(?) with higher RPM's might open up better on coyotes.
The 55g Sierra is one of the very best bullets on the market for coyotes, great on quartering shots of a 22/250, 22/250 AI, 223.
Also, Velocity is a major determining factor in kill power because of the temporary wound cavity that is created by the bullet's shock wave. If your velocity is low, then the temp wound cavity is smaller, rupturing less tissue, nerves, and blood vessels. As yardage increases, the size of the temporary wound cavity decreases meaning less tissue and nerve damage.
The very fastest velocty in a 223 with the 55's is achieved with Vitourvori N-135 and it is not unrealistic to expect 3450 fps out of a 24" barrel with a 1-12 or 1-14 twist rate with extreme accuracy, and in some barrels I have got the very best accuracy at 3500 fps with the 55g.
The vast majority of coyotes that I have killed with a 223 has been with a load of 26.5g of Win 748, with a 55g Winchester Soft point or Sierra 55g Spt at 3050-3150 depending on the gun, and I did kill an antelope with this load at 430 yards. This load did not destroy pelts, but with the low velocity, I never considered it a longer range load with 250 yards being about as long as I ever had to kill with this load.
I used the 55g Sierra Spt for the various 22/250's using win 760 with velocities of 3600-3650 which did a supurb job on coyotes (with a little sewing needed at times).
Coyotes are a tough critter to put down. I did a lot of bullet testing on coyotes after the fur market crash in the mid 80's. Simply hang up a coyote up in a tree or on a barb wire fence and shoot again, aim for hip or shoulder to check for penetration or surface splash. 1 1/4" orange stick on pasters from the local stationary store or Wal Mart work very well. Also, do your testing at different ranges...don't just back up to 50 yards and expect the same wound channels at ranges of 100,150, and 200 yards. I wish that I had kept records of my findings. If you do bullet testing on dead carcus', you will be amazed at your findings and how bullets you think are fantastic will cost you animals due to poor penetration, surface explosion on Ribs, hips, skulls, and shoulders.
Things have changed a lot, more folks are opting for AR's with very low velocities with quick follow up shots, and the 60g V Max would be a world class choice for that package due to it's great penetration and expansion in 1-12 or faster twists.