I own a Colt 4 3/4 and like it. It's a third issue, but I like it. The length of the barrel doesn't make a hill of beans diff. It's all about sight picture and handiness. Batt Masterson carried the short barreled Colt. That's nuff for me.
I'd like to own one of the 7.5 incher cause I want a pistol like the cavalry carried, but when I handle them it is obvious that the shorter barrel is quicker and easier to pack.
I don't know why you can't find a 5.5 incher. Keep looking. One will come your way.