A little bit of research led me to the sevenforums where I found some very good tutorials on optimising windows 7 by means of stopping unnecessary services and applications and some guidance on setting up Solid State Drives ( SSD ) to further enhance performance.
I spent the weekend tweaking my system in line with the tutorials and I am happy to say that it is now performing quickly once again. I just thought I should mention this experience as it made a big difference to my PC and the whole editing experience as a result. I'm sure I'm not the only one who has found themselves in a similar situation.
Asus PX79 Pro
i7-3820 & 16GB Gskill RAM, 64GB SSD OS Drive, 128GB SSD workspace, 2TB RAID 0, 2TB Backup, GTX-670, Win 7 x64 Professional.
PSE 11 & PDR10.
Nikon d70, d90, Canon G12, HD Hero, Panasonic HCV-500