I don't believe the wood grips from the older pre-lock Rugers will fit the grip frames of the newer ones with the lock, so you'd have to go aftermarket for one of those.
In general, the Ruger .44 Magnums have been more consistently accurate than their .45 Colts. Not that a .45 can't be accurate, but I've never had a .44 SBH that wasn't accurate and have had a couple .45 Blackhawks that did not live up to my expectations without some throat work and firelapping. That situation could have changed recently as the last .45 Blackhawk I bought was probably 4 years ago.
In weight, the .44's are all steel while the regular Blackhawk .45's have an aluminum grip frame. With the big holes in the cylinder and barrel the 4 5/8" .45 BH is one of the lightest Blackhawks they make.
For a plinking gun, I would offer up the new Flattop .45 Colt/.45 Auto convertible or maybe a regular Blackhawk .45 convertible. You can use .45 Auto ammo in it for mild plinking and factory .45 Auto stuff is cheaper than .45 colt ammo. The Flattop is built on a smaller frame so it handles a little differently but the grip frame is steel so it is actually heavier than the larger Blackhawk with same/same barrel lengths. Also kind of hard to find in stocking dealers, unless you see one at a gun show it's generally mail order only.
For the .44 Magnum you can use .44 Specials but .44 Special ammo is a low demand item and so is priced higher. If you handload, .44 components are everywhere, .45 components are around in sufficient quantity but could be scarce in some places.
All in all, a .45 Convertible Blackhawk might be the best for what you want. For plinking especially the ability to find cheaper .45 Auto ammo in quantity might be the deciding factor. You can still find the older Blackhawk convertibles with wooden grips on gunbroker for very reasonable prices.
