Have you backed off the adjustment nut all the way? I ended up cutting some off the end of the factory spring, and found that was all I needed. Didn't seem to suffer from appreciable creep.
The Brooks style kits is lighter springs and tubes. The tube acts as a shim to prevent the sear from fully engaging. Requires dissassembly and trial. There is a fully adjustable sear made, that allows infinite adjustment with set screws. Costs a lot more, but will allow you to set it exactly as you want it. The Brooks method requires taking it apart, installing the shim, reassembly and testing, and possibly repeat the process if you want to try another tube / shim. Cheap but more bothersome IMO.