Worth selling my current rmbp 2.6ghz model and upgrading?
Nope, performance difference will be minimal, but battery life will be better. If you don't need all day battery life then upgrading will be a disappointment.
The reason Apple need a 'special' CPU is because iris 5200 is close to 650m in performance but CPU performance has to drop below current 2.7 and 2.8 models. So Apple want both top end CPU with top end GPU integrated. Such a thing doesn't exist so intel is making something close to this just for Apple.
So current top spec rMPB may actually be a better buy at discounted rates for many people.
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