Hello all, I just bought a used Mid-2015 rMBP 15 to replace my older late-2013 one but it only has 256GB flash storage. My current machine has a 512GB module and I do need this large space. I read the new flash drive should be about 4x faster than the older one so I want the speed increase but a used 512GB flash module on Ebay costs about $400 and I'm not sure if it's worth the extra cost. I was wondering if using the slower 512GB from late-2013 in the new 2015 rMBP would be a bad idea. I believe the flash module will fit just fine, but will the speed difference noticeable in doing normal day-to-day work? Main things I do is web browsing, MS Office 2016 suite (Outlook and Excel), Windows 7 VM via Parallels and movie watching sometimes. I will end up selling the 2013 rMBP after deciding what to do so it will have a fast 256GB flash module if I end up putting the larger drive into the new one.