Do you have HP Performance Advisor installed? If not, I would strongly recommend it.
http://www8.hp.com/us/en/workstations/performance-advisor.html
I also recommend HP Support Assistant.
http://www8.hp.com/uk/en/campaigns/hpsupportassistant/hpsupport.html#.V_7LiMmRbgA
It will ensure your system is running with compatible drivers. Always a good place to start.
You could also consider downloading CrystalDiskMark. It's another good test tool. For comparison, here's my scores;
From L-R - 7200RPM 3.5" HDD, 480GB Sandisk Ultra II SSD, 256GB SM951 via ASUS Hyper M.2 X4 Mini PCIe card