I have a 3" SP-101, 3" blued GP-100, 3" stainless GP-100, and a 4" blued GP-100. They're excellent revolvers and with a lighter mainspring, the actions can be quite nice indeed. Feel in the hand is excellent, accuracy is excellent. Finish quality not great, but not terrible either. Definitely a good choice. I think you would be pleased with the GP-100.
Since you're a Smith-guy, by way of comparison, I would put the GP models between the K-frames and the L-frames, but closer to the L-frames, as far as impression of size and weight. The Smith L's do have a stouter cylinder and feel just a tad beefier than the GP-100's of equal barrel length do. My impression is that the GP-100 will withstand more heavy loads over a longer period of time than a K-frame .357 will.
As compared to the L-frame Smiths, however, I don't think the GP is notably different from an L-frame in durability... I'd rate them close enough to be comparable in that regard. I think a GP-100 is about the same as 686 for durability.
I feel equally well armed with either and enjoy them both, but the Smiths just have that extra something special which I personally really enjoy. Sooner or later you might want to have both Rugers and Smiths... why deny yourself the pleasure?
here's my 4"er:
I especially like the GP-100's in 3" barrel length:
In a 4" Smith, I've gotten great pleasure from the 586:
and the 681: