The 686 wins hands down for the purpose you listed.
The 66 is a great model, but I think the 686 will serve you better.
The extra weight would play against it if it were to be carried all day everyday.
In your case its just gonna make it more comfortable to shoot more!
I read a review once that said while it will handle it, the 66 was not meant to eat a steady diet of .357!
They said it would shoot loose quicker than a larger L or N frame. Quicker may still be many years depending on how much you shoot.
Sure its covered by the best warranty. That isn't an issue.
The issue is how it feels for you to shoot.
I have a Model 60-9 .357. It is a beast with .357 load. A bit to much!

I was looking at a 66 in maybe a 4".
My friend has a 19 & a 28 that I shot a few rounds of .357 through.
The 19 was a lot better than my 60!! But no where near the 28!
While it is not as big as the 28, a 686 would be a much more pleasant to shoot!
PLUS- It offers an extra round with the 686 plus!
Can we shoot .357 in all off them?
Yes!
Would we enjoy shooting a 686 more?
YES!!
Just my $.02! Ok maybe $.04!
