The Eastwest drive we have is a bit slower, so for large projects it might be too slow. So consider moving them to a faster drive.
OS drive size or cache is not really an issue. You will notice much snappier behaviour with an SSD connected to a SATA3 port. I use a 64 GB SSD for OS privately, with 3 hosts and quite a lot of plugs. I don't know why the OS drive should be that large.