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Still trying to nail this xo component to tuning.
So, if Butterworth shifts 90*, 12dB shifts 180*, 18*..270, and 24 back in phase again, then does 30dB bring it back to the same 90* as the 6dB slope? Or is it in phase but with different TA? How would a 30dB amplitude response differ from that of the 6dB and 24dB?

yeah 30dB/octave would essentially bring it back to 90 degrees out, but most people find 24dB to be plenty steep if you need a sharp cut-off filter.