So I've had my new Z77 motherboard for about 3 months now..and I'm just now realizing that this entire time, my SSD has been connected to a SATAII port and not a III, and I just switched it to the III port about 10 mins prior to this post, and I wanted to know, should I reinstall Windows to take full advantage of me switching?
Nope. To be on the safe side what I would do is reinstall the Windows AHCI drivers before swapping ports, you'll prob find the SATA3 has a different controller. AsMedia or Marvell etc. After you boot you can install the 3rd party AHCI drivers again if u want. However if you have a drive connected to the Gen3 controller, you can hook up the boot drive straight away, since the drivers are already installed.
For what it's worth I went from an i7 860 with a P55 mobo to a 4960k with a z97 mobo and never even reinstalled Windows and it found the drivers and worked fine. I half expected it to ask me to re-activate it, but it didn't. I'm on bog standard Windows 8.1 Home Basic bought from Amazon (blue DVD). I have reinstalled since but that was cos I got another hard drive, Windows itself was working fine and it needed a declutter anyway. Was (probably) quicker to reinstall than to mess about.