I have one of the Ruger Vaqueros in 44-40 that initially had cylinder with the well known undersize throats and neckspace. Sent it back to Ruger for installation of a cylinder with at least 0,429 throats and corresponding neckspace. I later polished out the throats to almost 0,430 -- true 0,429 bullets just slide easily, but snugly, through the throats. The bore is 0,429 groove-to-groove. Someone reamed a longer than stock forcing cone in this Ruger. The gun shoots any true 0,429 or 0,430 lead bullets really well. Does just as well with 0,429 jacketed bullets. Powders have been Blue Dot and 2400, with 2400 preferred -- these are my favorate for small grouping 44-40 loads.
This gun leads badly with 0,428 or smaller lead bullets, unless I put fiber wad under the bullet (BP loads only -- even leads badly with BP and too small bullets).
I have loaded ammo for this gun up to low end of 44 Mag velocities and all worked well. One of these loads has given consistantly the best groups ever in this gun. This is the best grouping revolver I have, with 240 to 300 grain bullets. I probably would not bother to load 200 grain bullets to the higher velocities. I would skip factory 44-40 ammo totally. Perhaps you can find a custom loader that will provide what you need, to your specs. The 44-40 loads that Alliant lists for Blue Dot and 2400 have always given really excellent groups in my guns.
Should I want a 44 caliber Ruger with adjustable sights, I might perhaps just get a 44 Mag and shoot it with lighter than full magnum loads. Because I already have loading dies, etc, for 44-40 I might get it rechambered for 44 Mag (think I recall correctly that can be done, just not the other way around). Might also look for a 44-40 cylinder and get it fitted, if it needs to be fitted.
Actually, my Ruger Vaquero shoots so well with 200 to 240 grain bullets, cast and jacketed, that I don't feel any need for adjustable sights -- which would be nice with heavier bullet loads. Most 200 bullet loads shoot very close to POA at 75 yards, 240s do so at 100-125 yards.
I would not buy a 44-40 with 0,427 bore because of the small selection of good bullets, especially jacketed.