I've got a 4 5/8" Super Blackhawk in 44 Mag, and I really like it. As has been stated, the 4 5/8" barrel makes 44 Spl loads a handful to hang onto. I have Vaquero's with 5 1/2" and 7 1/2" barrels. There is a big difference when the barrel is shorter than 5 1/2". More of a difference than I imagined. I was shooting 240 gr SWC at just under 850 fps, not too far off what a 45 LC would be.
I've got a convertible in 9mm/357, and it allows me to shoot cheap(ish) bulk ammo, if I want to. This also makes the gun easier to sell, if the time comes.
I think a 45/45 Ruger Blackhawk with a 4 5/8" barrel should be excellent. Loaded to normal book loads with a 255 gr Kieth, it's gonna feel like you are shooting something big. It won't be anything like a 357, trust me. The power factor on a 255 @ 750 fps is 190, and if you load to the manuals for T/C or Ruger, you can bump that to a PF of 250. Cowboy loads are around PF 180, and the gun will feel powerful enough.
45 ACP, for standard bulk, a 230 gr @ 840 fps, you still have a 190 PF.
If we were talking 7 1/2" barrel, then full power 44 Mag loads become a bit more manageable, and PF's in the 325 and beyond are factory fodder. But this is beyond plinking and fun IMHO.
Just my $0.02, for what it's worth.
PS: I would swap in a SBH hammer, and a Wolff spring kit, if it were mine.
Nitro