Probably good advice on heavy boned or thick skinned animals. However, my personal experience and the experiences of many others does not bear that advice out, on deer at least.
Over the past decade the standard .45 300 grain XTP HP has been used in smokeless muzzleloaders by Henry Ball and friends to kill over 1500 deer at muzzle velocities of up to 2100 FPS at distances of from 10 to 300 yards with excellent accuracy and terminal performance results. Myself, I have used the standard .429 200 grain XTP HP to kill deer at muzzle velocities of up to 1700 FPS from a TC Renegade for over 15 years with zero deer lost.
According to Hornady the 300 grain standard XTP HP is rated to 1700 FPS. In our experience it works great well beyond that point. On the other hand we have found the 300 grain XTP-Mag HP is very difficult to get decent accuracy from.
Since my stated range is under 1500 FPS I think the standard 300 grain XTP HP will do the job very well. If I go much higher I may use a hard cast SWC or a premium partition or solid of some type.