I think bringing to a boil just ensures that the extract disolves into the water as you pour it in. I would think at 170, you would be fine just stir well to prevent the extract from scorching on bottom of the pot.
I'm re-learning to brew after a 6 year break, so I have a lot of these little things that I don't re-call.
I remember now that I bring the tea to a boil while I'm warming up the liquid extract. Turn the flame off, poor in the extract while stirring. The extract seems to dissolve better/quicker and I can bring the wort to a boil easier/quicker. No empirical evidence, simply my feel.
We removed the steeping grains from the kettle,& brought the resulting wort to a boil 1st. When it got close to boiling,we got a wild,beercano hot break for about 3 minutes. When that was done,we then added the 1.5-2lbs of plain DME for the rest of the boil.