Back in the '70's, I worked in a lab developing E-3, E-4, and E=6. E-5 was and I think still is for the development of some of the specialized ektachromes. E-3 was, at that point in time, a professional process. It gave much better results than E=4. I don't recall developing any 35mm ektachrome via E-3, only 2 1/4 through 8x10. It did involve a re-exposure with a 250 watt bulb. The E-4 used a chemical re-exposure instead. E-3 was a fine process. If I recall, E-3 and E-4 were in no way compatible, chemically. Possibly at different temps. as well. The film for E-3 was always marked as being professional. E-4 was a crap process. The chemicals were very dangerous and the processed film tends to fade in 5 to 10 years, even if it has been kept in the dark and seldom projected. E-3 is much better in that respect. E-6 is much better still. I remember Agfachrome and Kodachrome having better blacks than E-4. There were two bright spots vis the E-4 process: one was Infrared film and the other was named, I think, Photomicrografy film. It was ASA16 and needed some serious green/cyan filtration as well. It was a higher contrast than any other color trans film at the time. Popular or Modern Photography tested it as being sharper than Kodachrome II ! Alas, all those brittally sharp and marvelously saturated slides and 4x5 chromes are faded past use.