Duck - the 19 and 66 aren't any bigger than the Security Six.
$350 - ish is way high (about $100 in my area) for a used __ Six Ruger. I'm not aware of them being offered in round-butt, but you could take your stainless 4" and have it modified to RB. You'll need custom grips then, I think.
My 4" Security Six wears Hogue Monogrips. Makes a very nice combination.
