Hi lesnicole, the configuration you selected for your iMac is perfect for your purposes. But my advice is to keep your working files and the OS on your main drive (the 500gb SSD in this case). But I know in many cases this will not be sufficient but, as D Fosse said before, in cases like yours there are 2 main factors who will affect your PS performances, ram and scratch disk. But lets say you are going to open a PSD file on an external drive the main part of the job will be still done on your RAM and SSD (if you have enough resources) and just when you will save your file you will face some slowness. Of course the best choice, as said before, is having your working file on your local SSD. In this case you can consider starting with the smallest SSD available on the Apple Store and then change it. (after market upgrades are easy, reliable and waaaaay cheaper than the original on the Apple Store).
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