It's more a matter of you and your ability...
A .454 with a scope is a 150yd deer killer in the right hands. With iron sights, 50-75yds.
Good shots with iron sights have taken game (even big game) well beyond 75yds.
Personally, I can ring the 200 yd rifle gong at my local range, offhand, one handed, shooting a stock (other than my own trigger job) 7.5"Ruger Blackhawk .45 Colt using a 250gr SWC handloaded to 1100fps.
Now, I wouldn't shoot at a deer at that distance, by personal choice, offhand. Rested? I believe I could make the shot, on a standing target. Would pass if moving. Again, my personal choice. At half that distance, I feel I could make the shot on a still target, easily. Been shooting that gun and load at all kinds of distances for 29 years, and know what it, and I, can do.
Its a matter of how well you learn your gun, and load performs at all distances you might encounter a shot. The main drawback to irons on a handgun, for long distance, is the relative coarsness of the sights. IT can be done, it can be learned, but its not as easy as it might be. Install fine sights, like on a rifle, and it becomes much simpler. Still a bit tougher than a rifle, but do-able with enough practice. The main limiting factor is your skill.
Assuming a 75yd max range because of iron sights is kind of reverse hubris. While its true that many people would not be able to shoot accurately beyond that range, there are many who can.
Also, when shooting, don't fret much over group size, in time, that will come. Concentrating on make ONE good shot at long(ish) range. Then make another. When you can make perfect shots at the range, realize that you are getting there, because in the field, its tougher.