I'm doing a JAL F award RT next February and our tier was JAL F >JAL J > AA F > JAL J. We were originally going for JAL J ex-US and JAL F ex-Tokyo for the same reasons. Every review/FT thread agrees that ex-Tokyo JAL service is the among the best in the sky.
The F awards are VERY hard to get for that time of year so be sure to be ready at T-330