For me, with my GP100, carried in a Kramer horsehide IWB: Upside down in a Galco 2X2X2 pouch, on a Bianchi Speed Strip: 6 rounds of Federal 158 gr HydraShok, on belt in 1 o'clock position; in a Tactical Tailor phone pouch, 2 X Speed Strips of the same; in a vest or jacket strong side pocket, a Safariland Comp III loaded with the same, for a total of 6 in the GP100, 24 on hand;
In my Security Six, carried in a Blade Tech IWB kydex holster: Same set up as with GP100, except using 125 gr .38 Special+P Remington Golden Sabers all around. Speedloader in pocket is a Safariland Comp II for a S&W K frame (which are slightly smaller than the Comp II Safariland makes for the Ruger -Sixes, but works just as well).
A field alternative holster for either pistol is my full-flap Bianchi UM84R, or a Hunter old-school leather w/securing strap OWB for the Security Six.
Best, Jon