If you're just looking for shooting fun, why not buy what you like? If it's steel framed and has a top strap, you've got belt and suspenders. Enjoy.
However, if you're looking for historical accuracy for Civil War event's etc. I don't think Remington made a 5 1/2" barreled 1858 New Army Model, but I could be wrong.
Cabela's is selling two of the Remington style 5 1/2" barrel guns. The one they're calling a New Army model has a steel frame and the other they're calling the Confederate model has a brass frame. Although the Remington style gun has a top strap which makes it stronger than a similarly made Colt-type 44 without a top strap, a .44 cal. gun with a brass frame would worry me, even with the top strap.
Having said that, I have a "Reb" Colt Navy by Pietta in .36 cal. with an open top brass frame. While its fun with light loads, I'm sure it would loosen up quickly if I fed it anywhere close to the 20 grain powder loads that the steel-framed Colt Navys are supposed to be able to handle.