Thinking of downsizing to 13". Thoughts?

Hey guys,

I currently own a 15" mid-2012 rMBP and and adore it. It's a specced up model with a 2.6Ghz i7 and a 512GB SSD.

As much as I love this machine however, I simply do not use the power. I'm not a photo/video editor or a developer. I sometimes make electronic music but that is it literally the only content-creation this laptop ever does (other than documents, but that doesn't take much power). I also own a rather powerful hackintosh (see signature), which performs significantly faster than this MacBook.

I'm also a student, so I have to lug my MacBook around more or less everyday. Now as light as the 15" is, its rather large footprint means that it fills my bag almost instantaneously, leaving me little room for books.

At first I looked at the 13" Air but I have simply been spoiled by the beauty of the retina screen, so thats out of the question. Which leaves me with the 13" Retina pro. Before I sell this machine and pull the trigger however, I have a few questions to ask.

How is performance in Yosemite? With the Intel graphics 4000 in this machine, the UI chugs a little and frame rates can hit rather low numbers.

Can the Intel Graphics 6100 almost match the 650m in my current laptop?

How is the 13" to travel with? Does it take up a large amount of space?

Is the 2015 model worth it over the older models?

Thanks!