While this is a "dated" post... I thought I would throw in a quick update and suggestion if anyone with this model comes looking for suggestions. Having had a 768GB SSD 15.4" Macbook Pro Retina (Early 2013), I can relate to the need/want for more than 768GB. I work with larger files quite frequently, and I'm impatient :) Even with SSD use, I find myself sometimes waiting (lol).
There is a new introduction to the market for SSD alternatives for the (2012 to Early 2013) A1398 Macbook Pro Retina (MacBookPro10,1).
Transcend's Jetdrive 720 - 960GB: http://www.transcend-info.com/apple/jetdrive/
$599+ (As of 6/15/14)
Buying one myself... will post performance reviews on my ifixit profile soon. Stay tuned...
If you like my post, please advance my score (seen above my profile). Thanks all!
J