I went looking for a GP at the last gunshow, but they wanted $150 more than the Security Six. I understand the GP was brand new, but I just couldn't justify the price difference so I brought home the Six. I've been waiting for a used GP to surface, but so far... no cigar .
I really like my Six and don't regret the purchase, but I already have 3 sixes and 0 GPs. One of these days....I'll find my GP .
Tony, if this decision was mine I would pick the Security Six 6 inch any day over the GP100. If you handle both you will find the Security Six is not as muzzle heavy. That is because of the half lug design. I never like the GP100 6 inch with of the full underlug. You might find a used GP100 6 inch with the half lug barrel design. Ruger only made them a few years. The Security Six is more than strong enough to shoot magnums. If would mostly likely out last you.