With proper bullet placement and at reasonable ranges, both the .45 Colt and .44 Mag will easily kill a black bear. I would prefer the .44 mag, but since the Vaquero isn't offered in .44, that leaves you with the .45 Colt. I'd guess that you will do far more Cowboy action shooting than bear hunting, so I'd opt for only one caliber for those shoots.

I killed my first black bear with a 220 gr cast SWC bullet from a 1911 .45 acp. It was a one shot kill at about 30 yds.

I killed another black bear with a 250 gr cast SWC bullet from a Ruger Superblackhawk in .44 mag. It was also a one shot kill at 30-40 yds.

Both were spot and stalk hunts on public land in Colorado and Montana.

All of my hunting and shooting is done with handloads.