I totaly agree with Catfish, and all the other replies added excellent tips. I also think recoil is, in large part, in the mind. Too much "stuff" going around about recoil this and recoil that. The best way to find out how much you can tolerate is, as you say, rent one and find out for yourself. Try a 454 Casual, a 445 Super Mag, 480 Ruger, 500 S&W if you can find them. That will give you a tight lock on what to expect. Recoil is a function of bullet weight, gun weight, velocity and powder charge, you can mix and match them all. Now if you want recoil, try a hot loaded Bull Dog 44 spectial at about 2 lbs loaded.
I've shot many different large caliber pistols and revolvers and I have/had several Ruger Blackhawks over the years. I like the Ruger style handle much better than the S&W 629. My present favorite Ruger Blackhawk was nipped off at 6" loaded with 265 gr Hornady's at near 1400 f/s. Seems to balance better in my hand. All my Rugersl sported Pachmayr grips and I used a padded glove. I guarantee racking off a cylinder full of 240's loaded max in a Ruger is much more pleasant than the same in a 4" "Dirty Harry".
I also rechambered an XP100 7mm BR to 284 Win because I wanted a "light", mo'bigga', carry gun for hunting brush and hills. Problem was it ended up weighing 6 lbs with scope and one round. 100-110 bullets put out about 16 ft lbs of recoil, but the muzzle blast and fire ball would almost barbaque what ever you were shooting at. Double ear protection was a must and just barely helped. I also shot 150-160 gr at 21 ft lbs. One shot would clear the game for miles around...and hunters too. A hot loaded 44 Mag with 240 gr bullet churns up around 16 ft lbs also.
Now to the point. Many times when I headed for a public range I would take the XP. There is always someone around making noise about recoil and how much they can handle. I would whip out the 284, load up a 110 and let'er rip. The muzzle flip would put the muzzle right in the middle of your forehead if you weren't holding on tight and had a locked elbow. Most of the time the noisy ones would drift away when I offered to let them shoot it. Once in a while I would get a taker. I would explain the hows and what for's, I didn't want anyone to get a crease, let them shoot a 110, then a 150, or as many as they wanted. Remember the recoil of the 44 Mag and the 110 were almost the same. Most of the time they were pleasantly surprised and the other "Big Dogs" didn't seem as bad after all. A good muzzle brake or Magna porting would have cured that muzzle flip, but I never got around to doing that project.
It just takes practice and consentration to get good at it. You might find the hype about how narly the recoil is just that, HYPE. Now a 45-70 recoil is a horse of another color, it REALLY has RECOIL....Hairy and scary you say...a 4 lb pistol with 300 gr bullet at 1400 f/s does about 22 ft lbs...just about the same as the 284 with 150's. Still vigorus, but it won't tear your arm off and it barely hurts for just a little while.
Hey, it's all fun....
Everyone I know who has/had a 44 Maggy single shot pistol always liked them. The longer the barrel and the heavier the pistol, the less the felt recoil. You might look at a 16 1/4" barrel if you're not set on a shorter one. That way you can shoot it as a pistol or a rifle. Best of both worlds.
