A 250gr bullet @~900 fps from a 45 Colt has been reported to take a horse right out from under it's rider. Like in the 40-65, 45-70, 50-70 and the like, but to a lesser extent, the 45 Colt's heavy and slow bullet will do the job as is. There is no reason to hot-rod the 45 Colt to hunt deer because deer are not all that hard to kill. If you already have a favorite load using a 255gr LSWC that load will do just fine on deer too.
My current favorite 45 Colt load for serious use is a 255gr LSWC bullet from Missouri Bullets over an almost Max standard pressure charge of HS-6. I'm loading in Starline brass with Winchester WLP primers. Other loads using W231/HP-38, Universal, Unique, A#5 and a handful of others will also work well if you already have a load worked up using your powder of choice. For range use I normally use W231 and a 250gr LRN bullet.
Good luck...