The thing is built like a tank and I have fired countless thousands of .357 and .38+P rounds through it without any problems.
The felt recoil is is very low compared to other .357 I have fired and it will, without a doubt, outlast the S&W686. Not to say the Smitty is not a great revolver because it is. The 686 is better in fit and finish, but the GP100 trumps in durability and is every bit as accurate.
You may want to get a set of Meprolight or Trijicon Night Sights because the factory ones aren't all that great.
Have fun with it - I certainly love mine and use it for as a truck/nightstand gun.
Mine is a Stainless, 4 inch model