Since I swapped out four 250Gb SATA drives for two 750Gb drives the startup time has been delayed by a matter of minutes as the ICH8R Raid Controller sat thinking about detecting the new drives. Changing the BIOS setting from RAID to IDE removed the problem completely, but alas no RAID.
I recently came across a known bug on the ICH8R Chipset where the controller would stall for 1.5 minutes if SMART was disabled on the drives. It turned out that the disks SMART status was set to Auto and this was enough to cause the delay. It is not obvious when the disks are in RAID configuration though as there is no setting for SMART. However if you change the Controller to IDE and set the SMART status of the drives to Yes then go back to RAID, this solved the problem in my case. Below are the details of my particular resolution.