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I'm not sure about Solidworks, but even the latest version of AutoCAD has no Retina display support. It looks a bit gnarly, and I generally wind up running it on an external monitor. If you use Bootcamp you can also just get the Windows version- it scales to lower resolutions pretty well (I use 1920x1200).

solidworks isnt even available for mac. i can run it fine (in windows through bootcamp) on my 13" pro though so dedicated gpu isnt a 100% necessity. will obviously be better though.
 
First off, welcome to the club as being a fellow CS major. I would definitely go with the 15". In our field of study, the more screen space the better!
 
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