Well, Dell have finally released a new set of Drivers (A04) and an AHCI fix for the the lock up issue. I have now applied both drivers and also latest BIOS (though this is not needed for this lock up issue).
My nVidia SATA driver is now version 126.96.36.199 and all looks good so far. The Bench Test within the driver gives results the same as the old A00 driver, much better than the A02 driver and the laptop has been behaving and rebooting as it should with none of the lockups experienced with the A02 driver. It is however my first day of use so only time will tell.
I will update after a few days of use to say for sure. Fingers crossed though!