I have a 512 GB SSD for OS and some games (I would get 1TB if it was today), 4TB 5400 RPM for data, and a 4TB striped array (2x2TB) for games. I suppose I have a large collection but the 4TB array is more than half full. Many games are 25-50 GB or more these days. So a total of 4 drives and this works really well for me. Of course in my stripe (built in Windows, which is a little faster than the Intel RAID 0) if one disk fails I lose it but since they are all Steam/Origin/Uplay games I can just re-download them.
Many games don't benefit that much from SSD - I put Battlefront on SSD and it was still slow as a dog to load. Some games really need to be on an SSD though, like Diablo III.