For some time the "classic" .45 Auto load has been a 230-gr FMJ or FMJ-FN and 5.5- to 5.7-grs of Win 231, as far as I am concerned. (Exact charge weight depending on other components and what manual you are looking at. )
I doubt the extra inch of barrel in the 6-inch gun is going to have any significant effect on powder selection so that combination should work equally well in the longer barrel.
i use a 200swc in mine and trying to decide between 231 and titegroup powder at present. the extra inch doesn't add much velocity when using fast burning powders. for a defense load. i would use a speer 200gdhp with either blue dot or acc #7. new autocomp powder shows some promise too.