E-6 films use a hardened emulsion and are processed at 100 degrees F.  E-4
used a prehardener solution and were processed (as I recall) at 85 degrees
F.  E-4 emulsions will melt and slide right off the base at 100 degrees F.

There were accounts a few years ago of processing E-4 in modified E-6
processes at lower temps.  Most popular film for the experiments was the old
E-4 process Infrared Ektachrome.

Unless you have a lot of film, properly stored, its probably not worth the
expense to experiment with the processing.

If you have rolls of previously exposed film contact one of the rescue
services that home brew all sorts of weird old processes.  Google came up
with these guys, the owner of Film Rescue used to post here a lot.

http://www.filmrescue.com/
www.rockymountainfilm.com

Kodak has published their official formulas here:

http://www.kodak.com/global/en/professional/support/techPubs/cis111/cis111.jhtml

alternatives:

http://www.mat.uc.pt/~rps/photos/FAQ_e4.txt

http://www.geocities.com/gselinsky/