I've just played
a 63 EB-0F,
a 69/70 EB-3 Slothead,
my 72 EB-U (a maple neck seventies EB-0 with added RD Standard pup)
a 03 Epi Elitist EB-3 and
a 05 Gibson SG-RI
side by side - all with flatwounds except for the Epi. There is not that much difference in the really deep bass they provide, but your ear is fooled when listening to a sixties mudbucker by the over-abundance of deep mids and total lack of treble plus - with the Slothead - the total lack of high mids too. It sounds deeper than it is. In my view/ear, you could approximate that Andy Fraser sound with all of the basses above (using the minibucker on the Slothead, because just the mudbucker would be too deep) - close enough for any Free tribute band. Some characteristics (using just the mudbucker except where indicated otherwise):
63 EB-0F (on board distortion not used): indirect signal with lots of midrange and traces of treble, fundamental not overpowering, throaty and overdriven), second loudest signal of all
69/70 EB-3 Slothead: indirect, woofy signal, fundamentals overpower everything else, overdriven, but the lack of treble AND high mids makes it sound less throaty than the 63 EB-0F, loudest signal of all, imagine an octave divider with the original signal turned down and just the octaved signal audible (also gives you a good idea of how indirect it sounds), if you use varitone position 2 with just the minibucker you still have a sensible amount of bass though lack of deep mids makes signal more bony, positions 3 and 4 add more mids, but cut bass beyond sensible use
72 EB-U: neither the bass nor the mid frequencies overpower the treble, the mids are no less prominent than either the bass or the treble, but not as throaty/overdriven as on earlier models, bit Ric'ish in character, while there is treble, glistening presence is missing, signal more direct than the sixties EBs, but lower output
03 Epi Elitist EB-3: a mix between the 63 0F and the 72 EB-U really, just a touch more well- behaved and even-sounding, but not boring, output higher than the 72 Gibson model, but less than the sixties
2005 Gibson SG-RI: warm mellow even signal, more direct than the sixties and seventies Gibsons, less overdrive, output higher than Epi and EB-U, most reponsive bass of them all