This radio came from the newest 2.11.605.9 ota and is said to have better speeds and 4g/3g handoffs. I just hunted it down to try it out myself, so I thought I'd share.
Here is a video showing how to properly flash the newly released, official MIUI ROM for the kindle fire. You will need the team win recovery installed first. As of Jan 2, everything seems to work except video playback.