Hard to say how much the underhood temp dropped but my intake temps dropped 10-15*. I had the high heat Grey coating. From what I understand the Silver does not withstand as high of a heat as the grey does but you would want to verify that.

The Equal length mani raised my underhood temps when I built that. Reason is obvious though, all the additional surface area. That mani I only wrapped with DEI heat wrap. My intake temps cruising were typically 108* and sitting in traffic were 113*. At the same time you have to realize I had SS intercooler piping which will absorb heat and stay hot longer than alum piping will. My intake temp sensor was in my Intake Manifold so at the same time there is a error percentage due to the sensor becoming heat soaked. I never got around to moving the sensor into the piping where it will read the most accurate. Chances are the lean condition I would get at idle on very hot days was becuase the sensor was heat soaked and not reading accurately. Food for thought.