This won't hold true if your RAM gets to the limit, and you end up creeping into swap space. If you do, everything becomes a potentially streamed asset! While certainly not ideal, you'll feel it harder on a HDD vs. SSD. Remember, you need at least 16GB of RAM for this monster, which these days is basically standard on most PCs (and about 70% of all Steam users as of August have no more than 16).