I have a 10 gallon Rubbermaid mashtun and I have been using 2-3 degrees for equipment heat loss and my temps have been right where I need them to be. If I was you, I would do the same for the first batch. Try using 3 degrees and you can adjust once you have some history behind you.
As it is, if I omit any loss.. IOW, if I say there is NO loss due to equipment, my strike water should be 167* for 6.6# grain.
I'm guessing it should be about 170* plus.. but not sure how much plus
When you say 170*, I hope you are guessing at the strike water temp, not the target temp...
I typically get strike water temps around 165-167 with the intent of setting in at 152* or so. It really all depends on the pounds of grain and volume of water and the equipment loss you know from history. Like I said, I would assume 2-3* for equipment.