Photoshop that's making it crazy loud?
It ended up better than it started. Everything from fans to ambient light sensor wasn't functioning on the first boots, but after a SMC and PRAM reset it actually cooled down and now everything is super stable. Now I only annoy over the few milliseconds of blinking whenever the M370X switches to Iris Pro and back. CPU sits pretty much at 40-50 celsius with HD streaming along web, mail and development apps open.
After a few days I have actually used the Macbook Pro more than the Macbook. I also feel the speed gap is wide between the models. Love the extra screen real estate, but hate the weight, though I am getting used to it. After thinking about how the next design will be, I think a thinner model may only come out with integrated graphics, but only if it manages to drive a 4k screen with the skylake chip without lag or stutter.
The rMBP 2015 with M370X is a future proof machine since it supports 5k. Nothing really out there in the Mac world right now delivers such great power and is "portable". Yeah, it is an old CPU, but there are no revolutions in that industry at the moment. The dedicated GPU will allow it to last at least five years. By then you should have been tempted at least twice to switch to a newer and better design.