R.P. just sent me an email to tell me that he found OS 220.127.116.11 around the intraweb for the 8300, 8310, & 8320. You can see what he has found at this link on BlackBerryFree or below:
UPDATE: Links seem to be down
I can say that OS 18.104.22.168 is extremely stable on the 8310 and is actually slightly improved from 4.2.2 in terms of speed.
Let us know if you find any bugs
NOTE: Do not install this software if you do not know what you are doing. It may make your BlackBerry FUBAR.