I always shoot for 160 to 165 on my strike water, reserving about 2 liters to heat or having chilled water that was boiled to cool as needed. I, also, preheat my mash tun with hot tap water to about 122. Pour the strike water in and check the temp and stir to cool if more than 10 above my mash temp, then dough in. Check the temperature in several spots to make sure that it is uniform and add the last 2 liters, heated up more if my mash is too low. Usually I'm within a degree up or down and don't need to add heat (benefit of living near the desert).