Dell MD3000i SAN Hard Drive Options

I am using a Dell MD3000i SAN in a 3 host iSCSI VMware implementation.  The current setup of the SAN is 14 146GB 15000 RPM SAS drives in a RAID 5 configuration with one of the 14 being a hot-spare.  I am running out of room in the configuration and I would like some advice on upgrade options.  Should I replace the current configuration with 14 2TB Near-line SAS drives setup as a RAID 10 or 14 600GB SAS drives setup in RAID 5?  Any alternate suggestions are welcomed also.  We run about 10 VMs in the environment with a mix of SQL, Exchange, and File serving.  There are about 50 concurrent users at this time in the environment.  I know that Near-line SAS is basically a SATA drive with SAS connections so there would be longer access times but i thought perhaps that RAID 10s boost in read and write times would help offset this.