Hello ! May I can share my point of views and prepare for sludge fist too as a healer (we have a paladin too as a tank).
I kind of understand the debate here about haste but honestly I don’t play paladin so… Here is what I think I understand.
So you choice is more dmg reduction more often rather than less reduction all the time (if you stay in you consecration).
So, you go sludge fist, as a healer I will discover the boss too. I need learn dmg pattern and who need healing. I would prefere learn that I need to take care of you constantly (if you have more mastery). Rather than have the surprise from one try to the other to have a tank one shot because for “this” specific hit you weren’t under your defensif. ( And don’t tell me you die from lack of healing when you die in less than 3 seconds xD)
I don’t know how good you are but I don’t think you will be able to manage 100% uptime on this defensive (specially at the end when things get messy).
Maybe give it a good full mastery and ask you healer to look at you and tell you what what they feel like “better”.