I will stay away from the lock/pre-lock part of the discussion, because it's my hope that my comments and experience will help the OP and not derail the thread.
The seven shot 686+ has a different double action trigger stroke than the typical Smith & Wesson K and L-frame (six shot) guns that I grew up on. It's noticeably different and without pulling punches, I hate it. The 686+ just gets my goat because it looks like the gun I know so well but it doesn't operate in a familiar manner.
In the 686 vs GP-100 decision, I'd choose the 686, and it would be close.
In the 686+ over the GP-100 decision, I'd so very much choose the GP-100 and have zero regrets.
I'd take an old, used 686 over a brand new, never touched 686+, and I'd happily pay more money for the older gun. I'd take any K-frame magnum over any 686+.
In my own opinion, finding an extra shot (from 5 to 6 or 6 to 7) is definitely a draw to a defensive or carry revolver. But in a medium/large frame revolver that you would use as an all-around fun shooter or an outdoorsman's tool? Give me the six shots and the proper amount of meat between chambers on that big, beautiful cylinder.