I believe you mean a GP-100 vs SPS-101. The GP-100 is a larger version of the SPS-101. I own one of each. My GP-100 is a stainless steel model with a 4' barrel and is chambered for 38 special/357 magnum. The SPS-101 is stainless with a 3" barrel that is chambered in the same calibers. To my knowledge, all GP-100's are DA/SA, are available in a variety of barrel lengths are made in stainless or blued versions and are chambered in .327 Federal to .357 Magnum. The SPS-101, I believe, is only made in stainless, has varying barrel lengths (up to 4"), are available in SA/DA and in DA only and are chambered from .22lr up to 357 Magnum.
If I misstated anything please chime in.