If you plan on putting an optic of some sort on the revolver, the barrel length is pretty irrelevant. A shorter sight radius is more difficult to shoot for most with open sights, but an optic takes all of that away. However, a higher velocity will extend your range a bit.

Can't go wrong with the FA as a choice, but budget alternatives exist that will shoot every bit as well, like BFR's offerings (in most cases). I know that a single-action is what you desire, but I wouldn't rule out a Super Redhawk. Every one I have had has shot well, the two new ones I have right now shoot lights-out.

As far as caliber is concerned, I prefer the flexibility offered by the .454 over the .44. You will not be limited by any means -- not that the .44 is a poor choice, the .454 just offers a lot more up top.