Ruger DOES make a great gun. But having had or shot both my opinion is that the S&W is that little bit better. Mostly this is based on the trigger feel. Even when fitted with spring kits the Ruger trigger has that annoying little "click" during the pull when the cylinder stop bolt is released. I find that annoying when I'm trying for a nice smooth DA pull.
But if you don't plan on shooting in DA that much then there really isn't much to make the 586 that much better, if better at all, than the GP100.
The trick, if you enjoy blued guns, would be finding a blued GP. Ruger makes primarily stainless guns. And in fact I believe that their "blued" GP is actually a stainless that is given some sort of blackening treatment that works on stainless.
If you simply can't wait for a nice used 586 to show up then look for the review threads on our recent Alpha Project guns done by Van-Man and myself. Short story is that we both like them. The Alpha is more in the K frame size though. So it has more in common with the Model 19 than it does the 586.
I found that in my own K frame guns that I preferred my .357's to be just slightly down loaded by about 10 to 15% off max power. The full house loads were OK. Just a little hard on the hands for a large number of shots during a session. Reducing the loads by a touch made them far more tolerable for steady shooting.
In the end though I likely shoot 200 .38's for every round of .357.
Those recent 7 and 8 round guns from S&W are nice guns. I'm all for more capacity. But if you want to use them in any competition matches read the rules first. You're often only allowed to load 6 or if you do load the max number you're only allowed to shoot 6. If you shoot more you incur a penalty of some form. So keep that in mind.