I find it more tempting to settle and improve the surrounding area. Growth and Techs will be super fast. You can hit them hard with attacking units. A big detour tech wise and growth wise for some enhanced archers? That it not even close the target. Make a better plan. No offence. Stonehenge only for some failgold if you happen to settle on stones. Edit: Dog Soldiers are quite good and should knock out a couple of neighbours. Edit 2: Those neighbours may even have built Stonehenge for you.