I have a pretty recent Windows install from a Asus P6T (i920) with 6GM of Ram, and a Nvidia GTX580 installed on a OCZ VERTEX 3 MAX IOPS SATA III drive. It will be going to a new Asus P8Z68-V LX Intel Z68, Core™ i7-2600K, and 8GB of Ram. This upgrade will give me SATA III from SATA II for the drive.
Should I reinstall Windows from scratch or could I just connect the drive and boot up and let Windows (and myself) update everything?
Well, I would prefer a clean install, but I am going to say this change will probably update it's self and work fine, I guess there is no reason to not try it. If you have issues, then you can always do a fresh install.