So, after going back and forth on waiting for the iMac Pro or long-prophesied Mac Pro, I've decided I'll probably get a 2017 iMac and fill it up to the gills with (third party) RAM to use as my next Logic Pro-focused machine. What I'm still on the fence about is how to approach the HD, especially as I have the better part of a terabyte of virtual instrument libraries to factor in. I'm not really feeling masochistic enough to go for a 1TB SSD, and I'm actually already running a clean version of MacOS from an external SSD right now in my current iMac. So I'm wondering if I should just plug that same external MacOS SSD into the 2017 iMac, and just choose a big Fusion Drive to dump all my libraries onto (as well as photos, mail etc) - thus never actually using the internal drive to run the OS or apps from? I guess my main concerns are: Does running the OS/apps from an external SSD come at any cost, relative to having them on an internal drive? Is that USB going to be bottle-necking me? Does having libraries on Fusion rather than SSD really matter much, or is having MacOS and Logic Pro on a SSD the biggest factor here? (bonus question) Assuming an i7 processor for both, would a Radeon 580 present any major thermal/noise problems that a 575 would not? Thanks!