The only thing you might get is some 100Mhz spec bump. Nothing else and even that isn't certain because Intel so far hasn't given any sign to release a spec bump before Broadwell. Given the general timeline they might skip this step and usually Intel updates their pricelist 2 months ahead of them showing up in notebooks. If you have the money now, buy it now. Otherwise you will be waiting till Broadwell.
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I feel like on 15".
1440x900 is just low res bad.
1680x1050 is much better.
1920x1200 is still better.
past 1920x1200 really does very little if anything, unless you are looking for it. On normal viewing distance I feel like, past 1080p on 15" does not offer much, I would really pay for. In games up till 1080p I see noticeable differences but higher isn't worth it, is kind of meehh.
Apple chose their retina res always because it doubled what they previously had not because it is some scientifically ideal resolution. If you compare 1440x900 standard res 15" the difference is huge. Compare a normal 1080p 15" display on normal viewing distance and color and contrast quality will be far more in your eye than resolution.
I never used 13" notebooks too long but I am guessing the golden res is much lower. 1440x900 on 13" is probably fine (kind of like 1680x1050 on 15"). 1280x800 on 13" I think is a too low. I don't think you will miss retina too much if you use it normally.