So I received my Altamont, full size, Letts style grips for my GP100.
Previously, I've used a Ruger branded Letts style grip that I received from Chigs grips, along with some excellent quilted maple panels. The Ruger branded grips and the Chigs panels fit together quite well and looked good. The problem with them is that I have above average sized hands and a high grip. The gun recoils back right into the web of my hand, and after about 50 rounds, I'm done. Often my hand would be noticeably sore the next day. Aside from discomfort, I'm concerned that I have some arthritis in my hands from previous injuries.
The Altamont grips don't feel noticeably stiffer to me. The Chigs panels didn't fit quite as snugly, and the bottom of the left panel would sit a little proud of the grip if I tightened the panel down too much. The fit well enough though and looked good. Here are pictures of the grips, and the area on the backstrap that is of concern.
Attachment 37130
Attachment 37131
I put fifty rounds through the gun and had the same issues. The load is a 158-grain hard cast SWC over 10.2 grains of Blue Dot. It's not a complete rhino roller, but it is certainly a magnum load. I was not able to discern a difference in recoil management between the Ruger branded grips and the Altamont grips.
The solution has been a set of Match Champion grips. As you can see in the picture below, there's quite a bit more material in the web of my hand. I experience no discomfort when shooting with these grips. .357 is a much more fatiguing cartridge to shoot than 9mm, but I can put a hundred rounds through the gun with these grips without pain.
Attachment 37132
Attachment 37133
I think this reinforces the truism that revolver fit is individual. When researching these grips, I found a post by BehindBlueIs where he talked about how the Match Champion grips were too big in exactly the same area where I needed more material. Fortunately, I don't have a huge amount of money tied up in any of these grips. The Match Champions work well for me, however, they do make the gun less concealable than the Letts. This isn't a huge concern for me as the GP100 is primarily a woods bumming and hunting revolver.
.38 Special +p loads work fine with the Letts. I would also bet that some more sedate magnum loadings like the 125 grain Golden Saber or 135 grain Speer Gold Dot short barrel, would work ok, although I've not had a chance to try them.