I follow the Denny Cheap'n'Easy method and add sparge water at 185-190F, stir, vorlauf, and sparge. I believe the fly sparging people use 170 degree water since it is constant, and will keep the grain bed at 170 once it reaches there. But you are correct that your water needs to be hotter than 170 to raise a 148-155 F grain bed to 170.
Let us know how the extended rest on sparge goes. Some have said it doesn't seem to matter, but 'm curious since I can never seem to get above 70% myself.