13", i7, 8 GB, 512 GB SSD?
I'm wondering if this is a logical purchase or just a "why not?" purchase. There is no way I am getting the new MB with the specs it has (and it's a 1st gen), and I'm supremely happy with my rMBP (mid-2013) that is fully decked out on specs. But a 12 hour MBA with full specs seems like a good purchase. Is there any reason not to go all the way on a light little tiger that will probably survive five or six years? Airplanes and meetings are delightful with a MBA.
My only reservation is the screen. I had an 11" MBA that I ended up selling because I didn't like the screen and battery life. But the 13" seems to compensate in some respects.. Even though the new MB has a Retina screen, I'm thinking it will be outdated within one year because of its sub-prime specs.
Kinda depends how important portability is for you...
I mean, at $1750, you can get a better performing rMBP. So value wise, it's starting to look a bit expensive. The MBA imo is awesome for being a really awesome base model laptop in terms of value. At $1k getting a 13' decent workhorse with insane battery life in a slick design is something that was impossible for everyone else until recently with the new Dell XPS and Asus.
But if you spend $700 extra for upgrades, I'd say you might as well get a RMBP. Better screen, better performance, new touchpad which might get a lot of software support the next 6 years.
Also the MBA 13' is only tiny bit
bigger than the MBP, which has thinner bezels and is a bit smaller. So the portability aspect is really in the weight, I'd say. The thinness helps, too. But neither the weight or the thinness are insanely different. At the thickest point it's a 1mm difference, that's tiny, and the thickest point is often what matters when it comes to fitting it in your bag. (it's not like you can stuff a mouse or keyboard or w/e at the thinnest point of the MBA).
The weight can be a deal-breaker, it's just a pound but it can be a 'magic barrier' for some. I don't know... if you're carrying books, a pound doesn't seem to make a big difference. If you're just carrying the Macbook, both are more than light enough.
For me the air is awesome because of its battery (12h vs 9-10ish) and awesome value at $1k. But I fear if you get the i7 that battery will take a small hit, and maxing it out reduces the performance

rice ratio for me.
So it really depends what is important. The main things to consider for me are:
Performance: MBP
Screen: MBP
Battery: MBA
Portable: MBAish (MBP is a bit smaller, barely thicker, but a pound heavier)
Value: MBPish unless you get a base model MBA
Throw in the touchpad, and I'd definitely choose MBP, unless that pound and 25%ish more battery is really important. It can be.
What do you use it for? If I had the money to max out a MBA, I instead just might get a base MBA 2014 for $800ish (or stick with the 2015 MBP). Sell it in a year, and get an upgraded 2nd gen MB, or Skylake rMBP 13" if the MB still isn't good enough value next year. Again really depends on your usage. I feel Skylake is going to be one of those events every 3y or so that either performance takes a leap, or battery takes a leap, or a bit of both, putting both the RMB and RMBP solidly beyond 10h of battery and with good enough performance for your regular consumer/pro, respectively.