For what it is worth, I'll try and accurately paraphrase the paragraph John Tinsley devotes to the 6 bath v 3 bath debate in his book.
Originally Posted by greypilgrim
6 bath gives the more neutral results and the Kodak process the most neutral grey. When absolute colour accuracy is required as in studio work the 6 bath process should be used. Outside work is a different story. An absolutely neutral E6 can give very cold results on film exposed out of doors in the middle of the day. In these circumstances the warmer results of the 3 bath processes are normally preferable to film exposed without filtration and processed in 6 bath. He goes on to show examples of six gray shades and alongside RGB and CMY for various processes including Tetenal, Kodak and Photo Technology, part of the Paterson Photax group. The film used for the test varied from Velvia to Agfa Chrome RS 50 and 100, Kodak EPX and EPR 64 and EPP100
Of course in looking at the colour squares the reader is relying on the accuracy of the colours on a printed sheet but assuming that any colour authenticity issues apply equally to all the examples, I could see no difference between Tetenal 3 bath or 6 bath.
While the book is now 13 years old and processes may have been improved, it may be worth obtaining a copy. A lot of what he says I suspect is still valuable in terms of processing procedures etc.
The book is called The Rotary Processor Manual and has an ISBN number of 0-902979-11-6. The publisher was R Morgan Publishing PO Box 11, Chislehurst Kent BR7 5RH
I am not an E6 processor as yet but I have looked throught the book fairly thoroughly and unfortunately he makes no mention of the respective longevities of film processed either way. This was not addressed in his 6 bath v 3 bath paragraph.
Hope this helps