Optimal drive configuration for SQL Server 2008R2
Variants of this question come up semi-regularly:


SQL Server build 
Help me choose a RAID level combination for a SQL Server 2008 instance
How should I configure these disks on a SQL Server for a BI configuration?


There are also occasional bun fights about the data/log separation "best practice".


Placing Transaction Log on Separate Volume [solid state]?
SQL Server - Separating data, log, and TempDB files on a SAN


Without more detailed analysis of what this server is doing, the same advice applies as given previously.


RAID 1 for OS
RAID 10 (6 disk) for data/logs/tempdb


There is rarely any point in a split with so few spindles available. A single array with a larger IOPs capacity will typically soak up the lumps and bumps of your workload better than 2 smaller arrays.

One variant that can be worth testing is putting tempdb on the OS drive. Only do so if you have a representative workload that you can replay repeatedly, to ensure a fair comparison of the configuration. If you go for this arrangement in production make sure tempdb growth is restricted so you don't inadvertently consume all free space on the OS drive.

Given that your OS drives are 7200RPM coasters, I'd be surprised if the tempdb on OS drive config bore any benefit.