Good posting and good discussion. But I think it misses one important thing about the nature of the LessWrong experience and community. We are not just 'into' rational belief and rational action. We are most importantly into rational discussion and rational communication.
I would add to your list of the five meanings of 'rational' above:
While one or more items from your list of five might be taken as the thing that we hope characterizes us as rational individuals, I think it is my sixth item that characterizes us as a rational community.
You see, I've seen the word "rationalism" used to mean all five of these things at different times:
Edited to reinstate that proposed solution, since this discussion is presumably finished.