They might as well take the "Pro" out of the MBP if they take out the dGPU. Even the 580 won't be able to hold a light against the next gen dGPUs coming out, and I highly doubt real world performance of the 580 will be anywhere close to the 370X.
Either way I will be quite disappointed if the new high end MBP has comparable graphics to my 4 year old 650M dGPU. The only way they can justify this is if they cut 500 bucks off the high end.
You know Apple's marketing department is doing an outstanding job when people take the names and denominations within their product lineup seriously/literally. There is nothing a photographer/architect can do on a XPS 15 Laptop, that a US$300 POS Dell notebook can't. They both run Windows, and thus run Photoshop/CAD/Production software, what varies is the speed in which the tasks are accomplished. I bolded that last fragment because their lineup is pretty much the same. The Macbook can run the same software as an rMBP. Both run Final Cut, Lightroom etc. But the Macbook will take a longer time to accomplished the same tasks. The "Pro" doesn't mean that the laptop is suitable for professionals, it just means that it is relatively better and faster than the one below it. The user makes the most of the laptop, not the other way around. You make the laptop as Pro or amateurish as you want to, the purchase doesn't define the user when it comes to notebooks. The plethora of rMBP i have seen in the wild are from people (teens mostly) sitting in Starbucks browsing the web/writing a word document. If we go by the typical definition and stigma the "Pro" name has, none of them should have bought it because a US$300 POS notebook can achieve the same thing that their luxury US$1299-1999 notebook can. My brother (16) made my parents buy him a 15" rMBP 2015. The reason?....just because it looked nice according to him.
Oh and remember that they killed the dGPU in the entry 15" Macbook "Pro". They decided back then that Iris Pro reached acceptable levels of performance, they didn't drop the name.
Macbook<Macbook Pro. Functionally the same, just faster. That's it. No over-complications. There is no international standard that regulates how many ports, cpu speed, or ssd capacity a "pro" machine should have to be called a "pro" notebook.
Sorry for the long post. The first part about marketing and such wasn't directed entirely to you, it was to the forum in general.
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