roll rate is hard to use, you need good SA and moe importantly a very good idea of the E state of your opponent. In th case of the FW190, the latter is really really important, since timing (like a lot of things) is key. If you start rolling too early, you are just spinning aound infront of the con while he waits for you to lose all your E. Too late and well. . . roll all the way to the ground.
The thing about the scissor is to understand what you are trying to accomplish in the maneuver. I think this is true with most things, but the scissor is not a pure defensive move, its a cheeky way to reverse a deadly situation into a kill for you, and the more agressive and confident (and gas happy) your oppenent, the easier it is to get him. Essentially, you are creating a situation where the last 5 seconds of the opponents life is 'oh no. . .' which is satisfying. I think its a simmilar kind of satisfaction 109 pilots get when they do that magical roap, twist, kill move.
there are a couple of good pdf guides to how to execute a proper scissors, explaining the different kinds (vertical scissors up/down, flat and rolling, etc) - I recommend you look for them. (I have some, but i can't host them from my curently country)
sorry for the small rant - gl