First of all, you have a rather large flaw in your comparison. While the Cobra stuff was upgrade, the pad was a huge downgrade. You are talking about going from a pretty aggressive performance pad (EBC Green) with something that's not meant for any performance driving what so ever (Reybestos Ceramic). Ceramic pads have a very shitty working range, and they have a very low friction coefficient, so what did you expect exactly? That's like you saying that you went from 245 to 275, but 245 was Azenis and 275 is all season tire, and since your all season 275 does not grip as well as max performance 245, there is no reason to go wider.
Secondly, there is a LOT more to cobra setup than just head dissipation and larger pad. The whole point is that the pad sits a lot further from the hub, which gives it much more torque (think leverage here), and therefore stops the car faster as well. When I went from 99 PBR calipers to a Cobra kit, I saw a HUGE difference in bite, both on and off the track.
To OP: I went through a ton of setups. I've had stock cast iron, 99 PBR aluminum, Ford Racing Cobra kit, and currently running Brembo. I will tell you that as long as you are using a good performance pad, every time I stepped up to a new setup, I have felt performance gains. The only downside that I can think of is that going to a larger rotor will give you more rotational mass, and might slow the car a bit down in the straight line.
