From what I have been told by my dealer to took a 17 HMR on a p-dog shoot, it will not make clean kills on the little p-dog past 75 yards, so on a groundhog I would not use it at all, regardless of range. I've killed too many hogs with the .22-250 and they can be quite tenacious, and IMO the .17 HMR does not have what it takes for g-hogs. I don't care if it is a varmint, I want a clean kill. I cannot stand to make an animal suffer, no matter what animal it is.
I like Ruger 77-17 tgt a lot, it is incredibly accurate, but I will limit its use on squirrels and rabbits. Regarding the pistol, the only thing that really matters is do you want it? I plan to get one just for the heck of it once they make it in stainless to match my rifle (I'm sure they won't make it-the pistol-in target gray, but ss will be close enough). I doubt it will ever be used against anything more alive than paper, but it will be fun to have. My Super Single Six is over 30 years old, so it has had a lot of rounds through the barrel. It was never a tack driver with either cyclinder, however, I consider it plenty accurate enough considering its intended purpose. If I want to shoot super small groups with a .22, I reach for the Mk I or Mk II target pistols. They shoot rings around the SSS.