For sure, statistically three shot groups can be insignificant for sure, however I tend to take it for what it's worth and most times roll with 3 shot groups at 100 for load workup to eliminate wind error. If the load continues to produce each time out, I know it is a winner. When i have a new barrel or rifle, i spend much time getting to know how it shoots and usually break it in and just have fun shooting up to about 100-150 rounds because they all seem to speed up considerably after break in.
I sight in at 200 with hunting rifles then consistently test in varying conditions out to 1500. Like you, I am lucky to live in a place where I can leave the house and be shooting out to nearly a mile in a few minutes and have great friends that enjoy it too.
I agree that cold bore testing is what matters most for hunting. Many times I will take 2-3 different rifles and shoot two shots each on a 16x16 steel or shoot spots on rocks and record them with the phone through a spotter, then go home and do it the next week. This is great practice for wind and temp/weather data can be obtained at the same time. What I have learned most from this cold-bore shooting is my limitations in a hunting scenario. No or low wind means a definite possibility of longer shots, if needed, for me. Crisscrossing wind patterns up different ridges and terrain cause me issues, but high winds typically mean a person might allow a hunter to sneak closer than normal in many cases.
I agree ES/SD are important, but I have seen times where a rifle/barrel will produce single digits every time and group like a shotgun. Keep us posted on your data thread! Good shooting to ya!