The speed six, which is a security six with fixed sights, is quite a bit different internally than an GP100.
Personally, I like the trigger pull of the older stylespeed/security six better, but I have 3 of them (2 3/4, 4, 6 inch barrels) and I might just be more used to the feel.
Anyway, it is a good gun that is really hard to wear out or break.
You didn't say if it is blue or stainless. One odd thing that happens on the blued versions is that the plunger that locks the trigger group into the frame tends to build up corrosion, where the stainless versions do not. I am assuming that it is a case of dissimilar metals. Whatever the cause, take it apart once in a while and keep a bit of grease or anti-seaze on the plunger. Rugers are cake to take apart anyway (especially with the special green-handled ruger trigger-group-plunger-pusher-tool that Brownells sells).