Looks to me like your goals are somewhat contradictory. With that bullet weight in the .45 Colt it seems unlikely that you'll even break 1,000fps, without having the loads batter your poor Smith to death. Slow them down enough and at some point they might not stablize too well and the trajectory will resemble a mortar, instead of a bullet.
The recoil from these big slugs might take some enjoyment out of the shooting session also.
Not sure what your definition of long range is, but I've found decent results in the 200-300 yard range with a common 255gr. SWC at around 1,000fps in my Bisley. No fantastic group sizes to report, just shooting at big rocks. I'm sure for the ultimate in accuracy a LFN would be the way to go.
One person's opinion... I've shot a Smith but don't own one and the same 1,000fps / 255gr. load was quite manageable, recoil-wise, to me.