That is a reverse sear and it works like a charm. You can even sear on your gasser after slow cooking the steaks on the WSM, but if you cook them to 170, then they're ruined anyway - in my humble opinion. That is WAY WAY WAY past even a well-done steak.
Take the thick cut steaks to about 110 on the smoker, THEN whether you sear them on the gas grill or direct over the coals on the WSM, just do about 2 minutes per side to get them to what I consider to be medium rare. I have learned that while thinner cut steaks will continue to cook for about 5 more degrees after coming off of the grill, nice thick-cut steaks will continue to rise as much as 10 degrees.
For my preferred medium rare, I cook the steaks to 110, then sear for two minutes a side, which puts them at about 120. I pull them and they finish right around 130, which is medium rare in my house.
Try it - I think you will like it.
Pat