Modern singleshot rifles can be scary accurate if built properly. Sub-MOA accuracy is usually not a problem with most provided the shooter, ammunition and rifle is constructed without a major fumble. I've not had a Ruger No.1 yet that wasn't capable of it, provided I did some minor "tweaking". Tweaking would consist of trigger work, maybe some forearm pressure relieving or adjusting of the spring. I've heard, but not experienced myself, of quarter ribs having to be relieved a little on back end against the action.

It would be more of a guarantee to start a build from the ground up with a Dakota, Hall, or Hagn for what you are looking for than a mass production barrel and action like the Ruger, it's just the nature of the beast. For top flite accuracy, I don't know of anyone using factory components without some renovation.

Also, for me and what you are describing, lugging a rifle into the desert mountains in high temps, I'd want a relatively light rifle, not something the Ruger comfortably is. All their rifles are built around one action. From the 22 centerfires to the 458's, they all use the same action. A small action Hagn could get the weight down much easier without sacraficing anything for strength or accuracy.