The 416 fires a little hot out of the box, but after a good thousand+ BBs fire through it the spring should settle down, key word being should.
Here is a link to a spring chart that was created by ILLusion.
It is old and does not have all current day brands but its enough that you should be able to get an idea of how and springs are labeled what they are. Even though its not in the chart, a modify S100 would put you in the ballpark area of 360-370.
I am not extremely heavy on knowledge about hop up rubbers, so I will let someone with the appropriate knowledge handle that area. If I may make a suggestion though, the guarder clear hop up rubber set is an excellent choice for anything firing under 400FPS.