Double check the data in the Hodgdon's Annual (since it appears that's where you're getting your info), there's a typo and the 158XTP is listed twice. Once with weak loads using fast pistol powder that just isn't appropriate for the cartridge and aren't magnum loads at all and once with actual magnum powders that are appropriate to the cartridge and bullet weight and significantly more pressure and velocity. I wouldn't really call H4227 a real rifle powder. Speaking from experience, published loads essentially call for a full case of slow burning pistol powder which maxes out the pressure while burning slow enough to sustain the pressure and also fast enough to not be outpaced by the high expansion ratio. Going with a slower powder will not reach max pressure and will not sustain pressure either.
The 180gn load is probably a better long range bullet, but even it is limited in range and depending on what you're hunting the 158 will do a very good job as well and shoot a little flatter. If you have a Blackhawk with a 6+" barrel the 180gn load is suitable for it as well and the Hodgdon's data shows over 1400fps from a 10" barrel and Hornady 1150 from an 8" Python.
If you're going to tout "right tool" use the right tool.
