For standard Colt loads your only looking to get into the 850 - 1000fps range. There are several powders which will do this easily and are pretty economical per load. You mentioned plinking, so that is where these would be at their finest from your longer barrel. I would also suggest looking into some of the cast bullets which are available from several production casters. They are a bit cheaper and will provide not only some nice low recoiling rounds but will also do a number on deer or other critters.
Here are a couple of places to browse,
Montana Bullet Works
Missouri Bullet Company
Penn Bullets
Cast Performance
Personally I have used the Cast Performance 269gr WFGC and it is a real performer at around 1400+fps. I used them in my 454 until I got to shooting it too much to afford them, and I broke down and started to cast my own. I'm now using the Lee molds for both my 45 Colt and 454. I have mold for a 255gr RFN, one for a 290gr RF, and another for the 300gr RF, and they all shoot like a dream from the Colt. I have settled on the 255gr mold for it however as with my WW alloy they come out at 260grs right on the money.
I figure with a decent charge of 231, Unigue, or 2400, I should have all the basis covered with one bullet for the Colt.