Pull all cards, clear the bios (battery pull), reinstall all cards. Sounds like contention for a resource. Raid card cache policy would not cause keyboard delays. Do you have a SATA  to hang off the motherboard interface to install on, with the Perc removed to rule out the Perc.    
Windows Server on a well equipped R710 II is very slugish as though something was taxing the box: Yet Task Manager and Resource Monitor don't show the CPU, RAM or Network being taxed. I've been working on this for a few days now and I'm nearing the end of my rope: At this point, it doesn't appear to be hard drive specific but at this point I'm thinking possibly: Aside from that, I really don't know where to go from there so I'm reaching out for some guidance.Anything you can think of or recommend would be greatly appreciated.  Server Stats:
Help Troubleshooting Sluggishness on R710 II Running Windows Server