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Paying for i7 in 13" Macbook actually makes a very little sense (only about 7% higher performance in sunny-day scenarios).

Extra 8GB of RAM could make some difference, but it depends on the use case. For video I don't think it is that important.

If extra $350 can get you closer to a 15" model, it can actually make a whole world of difference.
 
What about the 16GB RAM? Worth $350? I'm guessing not.
I think not. 8GB is more than enough for most people. It sounds like you already made a good choice!

I have a 13" i5 (2012 2.5 1TB 16GB) and a 13" i7 (2011 2.8 480GB 4GB). They run about the same. I can't detect any difference in performance. The 2011 is my media server (music, movies and netflix) connected to my stereo and LCD projector. The processor is probably very under-utilized. My 2012 is my main machine and I use Aperture, Photoshop and iMovie mostly.

I just downsized from a 2012 15" rMBP (i7 2.7 768GB 16GB) and I honestly can't tell the difference between this and my 13" i5.
 
Audio software always benefits from more physical (and virtual) cores. Logic X in particular can use every available core, up to a total of 24 I believe.

For intensive virtual instruments/plug-ins, you'll want at least 8GB RAM. Aim for 16GB if you're keeping the Mac for more than a few years, since you're covering yourself with headroom for the future. Larger SSDs also tend to have faster transfer rates due to the way they work, so as big an SSD as you can afford is good. If you're recording real instruments across a dozen or so tracks, you can get away with less. Remember, you can freeze tracks in nearly all DAWs if you desperately need more performance from what you have.

Sadly, these days you have to buy all these extras up front. With my 2011 15" i7, I added a 512GB Samsung SSD and 16GB RAM a couple of years ago for not much money and, honestly, don't feel any need to upgrade for pro audio work. I want a Retina display and USB 3, but that's really all. I'm waiting until we get new MBPs with TB3 and USB-C ports, and even then I may wait until the second iteration of that design (always a good rule with Apple stuff, generally).
 
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