To add to @TheTick 's comment:
Our volumes are divided up like this:
2 SSDs in RAID1 - Windows Volume
6 HDDs in RAID5 - \BigFix Enterprise\BES Server\wwwrootbes (bulk storage)
2 SSDs in RAID1 - \BigFix Enterprise\BES Server\* (FillDB and others)
2 SSDs in RAID1 - SQL DBs
2 SSDs in RAID1 - SQL Transaction Logs
2 SSDs in RAID1 - SQL TempDB
We try to install & update all software through BigFix/IEM, so for us, \BigFix Enterprise\BES Server\wwwrootbes is very large.
We have a similar number of endpoints, but our main performance issue seems to be due to the number of simultaneous console operators we have and the very decentralized nature of our IT structure. A recent patch for the console we are testing seems to be helping.
Update: I would recommend PCI-E based SSDs like the Intel P3700 for SQL & FillDB with frequent backups.