Usually a single infusion at 156F means you are aiming for a beer with more body and a sweeter finish, since this temp favors the alpha amylase which makes starch into big chunks that aren't all fermentable. By doing your step mash protocol you'll get a more fermentable wort resulting in a drier beer with a slightly higher ABV. Since you have 12% crystal in the recipe I think you'll still have plenty of sweetness.
Martin, I've begun doing some short protein rests to try and get my beers a little more clear, especially those made with TF Maris Otter. I also played with step mashes this weekend, my first attempt was poor and resulted in 64% efficiency, the second went better and I got my usual 75%.