I have no opinion on this discussion as I have no knowledge of 20b swaps, but I can say for sure that the Series II (2009+) RX-8 transmission is from the MX-5. It was my (possibly mistaken) impression that it was stronger than the MX-5 version, however. I believe I read that in some of the reviews of the 2009 RX-8. Series I RX-8 transmission is not from the MX-5, but an Aisin transmission (
http://en.wikipedia.org/wiki/List_of..._transmissions).