Thanks for the link but I couldn't find anything helpful there.
However, I have now resolved this:
In the 'storahci' tree there is a 'startoverride' entry. It is also necessary to change this to 0 after which you apply the old patchedcode in Terminal in OS X.
However, on reboot I found that almost everything was inop, including my mouse & keyboard. Inspection of 'Device Manager' in Windows showed that one of the USB Root Hubs was disabled:
I went to Update Driver >Browse my computer>Let me pick>USB Root Hub the restarted the computer.
All now working in AHCI mode
Thanks SkyriderUK... this worked for me.
I was wondering why my Macbook Pro late 2011 was running a bit slow, considering I had installed a Samsung 830 512GB SSD. It was because AHCI was disabled (see below for performance before and after).
However... I did run into some issues.
Firstly I want to make the process clearer for others as I had trouble understanding exactly what to do:
1) Follow the Steps on this page except Step 8: http://www.ithinkdiff.com/how-to-enable-ahci-in-windows-8-after-installation/
2) Restart and go into the Mac side of your computer
3a) To copy over the "patchedcode.bin", make sure you boot onto an external USB key or DVD. I used the reinstall Mac OS X DVD that came with my computer.... loaded this but didn't install. Just accessed Terminal using the drop down menus at the top.
4) When I rebooted into Windows 8 for the first time, my computer wouldn't load. Error screen during startup. Had to reboot.
4a) One the third boot of Windows 8, it offered to do a "roll back" for me. I did this. Still didn't work ie. couldn't book Windows 8.
4b) Luckily I had Parallels on the Mac side. I loaded my Bootcamp install of Windows 8 via Parellels on the Mac side. Because I did a roll back, I had to make the necessary registry changes again outlined in http://www.ithinkdiff.com/how-to-enable-ahci-in-windows-8-after-installation/
5) Then I rebooted back into Windows 8 and it loaded this time for me. Thank goodness. Now AHCI is working!!!
So how it my system running? Was it worth the effort?
See image below. Dark blue is running AHCI, light blue is before running AHCI. A big difference!!!
Hope this post helps others.