I wanted some advice on how to best configure my PERC 6i controller. Currently there is 8 SAS 146GB drives in the system. 
2x146 Raid 1 C drive (OS)
5x146 Raid 5 D drive (Data Storage)
1x146 No Raid E drive(Cache)

The reason I am asking is because of high disk transfer numbers especially on the C drive. Would it be beneficial to use all 8 drives in a raid 5 configuration? Would that improve performance?

 I changed the policy from write through to write back and it seemed to help some. The system is mostly used for read access during business hours and only updated nightly.

The server in question is a R710 with 36 GB of ram 2 x quad core cpu.
Any advice would be appreciated.