Since you said youre not gonna reload id say 44 mag. There are lighter 44 mag loads. The barnes vortex are very mild, the hornady 300 gr are mild. I could name others and feel that you wont give up mild loads going to a 44 mag. If you want to take advantage of the highest level 45 colt loads that are factory loaded there is no point in going away from the 480 ruger anyway. Keep in mind, as factory loaded imho and experience you gain nothing going with the 45 colt vs 44. The one with the better bullet wins and is more effective every time. A 44 will flatten all the game you have listed with rhe proper load. To fully take advantage of what a 45 colt has to offer is a handloading only proposition and would require a 5 shot cyclinder. Once again, at that point you might as well just get a 454. Mild loads exis for that and theres several that have not as much recoil as heavy 44 loads. They also tend to be the cheaper rounds as well.

You will hear alot of 45 vs 44 mag but in real life the better bullet wins, period. You can raise the 45 to a slight ballistics notch above. If you want an easy shooting 44 factory load i can point you to it and it will save you some money over the 45 colt as well. I also feel the standard bisly 44 tends to be a more accurate gun and ive seen more than a few 45 colt bisleys with crummy throat dimensions, not so much with the 44.