This debate raged a while ago when devs first began introducing ext4 into their roms. I can answer some of your post by saying that ext4 organizes your files much more efficiently for our flash based storage. RFS essentially treats storage like it is platter based (like a hdd). Without getting into much detail, ext4 locates and organizes data better than rfs. Ext4 is still better, even with journaling on.
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