My 2012 MBA has an i7
Yep - I was mistaken. The processor upgrade in the air doesn't just give you the faster 2 GHz clock - it also goes from I5 to I7. So that brings it even closer to the 13" rMBP. And you can get that processor in the 11" too if you want for max portability.
The 13" rMBP is a lame duck - just too crippled to justify itself. It isn't even about the pricing model for me, it's about the lack of BTO options at any price. Just as an 11" Air comes in at just $50 less than its 13" sibling when optioned with the same RAM, SSD, and proccessor (and GPU, which they share by default), I would similarly pay nearly as much (or even equally as much to be honest) for a 13" rMBP optioned with the same kit as its 15" older brother. But you can't have it that way - not even close in fact. And that is just a damn shame, really.
Now I have to decide whether I go with the maxed out 11" Air or move up to a the 15" rMBP at twice the damned weight. Ouch. Thanks Apple. I guess it comes down to whether the Air with integrated graphics and just 8 GB RAM can adequately power two 2560x1440 displays (in clamshell mode - I don't need the built-in display while at my desk) as well as be powerful enough to allow me to do my Wintel business app development.
Maybe, what I need to do is investigate whether there are other Ultrabooks out there that have 16GB RAM option, Q-core I7, and discrete graphics, and can also power two 2560-by displays. I am guessing not since, without Thunderbolt, they'd need two video outs capable of that resolution - I.e. Displayport, Dual-link DVI, or appropriately capable HDMI 1.4. It seems unlikely, but maybe there's a nice, small VAIO or something out there with my name on it.
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What additional functionality would that be exactly?
A higher proccessor clock, a second TB port, HDMI, and the Retina display. That's it.
Oh, and the dual mics, four speakers, and digital audio out. You're sold on the Pro now, right?