We like both, own both .4. the gp100 is heavier so it can help the shooter tame the recoil.---Mostly false. The GP100 and SS, with matching barrel lengths, are virtually identical in weight, due to the frame design at the grip.
FWIW, mg357 was right about the GP100 being heavier. A 4" Security Six weighs 33.5 ounces. A 4 " GP100 weighs 41 ounces.