my exp with the single piston ones is that they vary alot in how far the square ring/tolerances etc will retract the piston therefore how much drag you see at rest. rebuilt calipers are cheap & pretty dependable. I'd consider getting another pair of parts house rebuilt calipers. that's what I did on my last deal & the drag was halved. it'll never be close to being free/as you know its the nature of the beast.