I made my choice just recently. Between .357 and .45 Colt I chose the latter in a New Vaquero. I can load this to Tier II levels (280 grain bullet at over 1000 fps) but settled on ~850 fps with a 255 grain bullet.
In Elmer Keith's "Six Guns" he stated that the .45 Colt with a 255 grain bullet loaded to 1000 fps was strong enough medicine for anything in North America. When he asked Smith and Wesson to design the .44 Mag he wanted ~250 grain bullet at 1000 to 1200 fps but Smith and Wesson loaded it even hotter to over 1400 fps. Elmer used the Colt SAA in .45 Colt with loads just over 1000 fps.
The New Vaquero, with a 4 5/8" barrel is really quite sleek compared with the Black Hawks and this is why I chose it.