The main differences are.
- The trigger assembly is easily removed as mentioned above on the MKIII
- The bolt uses the 3-position safety on the MKIII just like the AW/AT/AX rifles
- The skins are also a little different but not hugely so. The MKIII skins allow you to remove just the section around where the trigger is for easy trigger removal
In order to get the links that point to the old .info site to work just change it slightly...
from:
forum.snipershide.info/showthread.php?t=120933
to:
www.snipershide.com/shooting/showthread.php?t=120933
The changes from the MKI to the MKII were much more substantial with the most notable being the change to the AICS magazine in the MKII.
ETA: Honestly right now with the prices that the MKIII's are selling for I would watch for a used AW. It will cost you $400-$500 more but the AW is a very nice rifle and the double feed magazines are awesome! Either way make sure you get the folder.