So first of all it’s up to you how you setup with different gear weights.
Resistances are not absolutely essential above 28,000~ so the damage mitigation you get above that is minimal. For very hard fights with a lot of damage 7 Heavy is going to maximise your damage mitigation as long as you don’t go above 33k resistances. If you are using the Heavy Armor Skill Immovable you need to use 6/1 to optimise the use of the Skill but also make it so that you can still move but are still very Tanky.
For anything else 5/1/1 would most likely be the best balanced setup overall because it will improve your sustain in a range of different areas. 5/2 is good if you just want to focus in on a certain armor weight passives that you feel are better than another and this is a valid option for certain situations.
As a Tank you always need to have at least 5 Heavy Armor pieces or you lose the Revitalise and Rapid Mending Passives and Tanking becomes more difficult so it’s not advised unless you are running easier content and are specing as a Hybrid Tank.