You are not going to get 1 hour out of 1 layer of 5/8" Type X.1 hr fire rating
You can achieve a 1 hr rating with 1 layer of 5/8" Type X within a floor assembly. Usually the UL listing incorporates the components within the floor or roof assembly.How can 1 layer of 5/8" Type X give you a 1 hour rating, when you only get 20 minutes for 1 layer???
Any of the decoupling systems rely on the flex of the steel. This is true for RC-1 or resilient clips + channel. In both cases we want the steel to flex. 25 ga. flexes more than 20 ga. so all things being equal, you will have greater sound isolation with 25 ga rather than 20.the answer is yes you can. use 20 ga. RC.