I developed some c41 at room temp. specifically expired E3 and E4 ektachrome. but also some random recent c41 films I added to the run. Try 65-70 degrees, I bet you can go lower but would then consider extending development time further. sounds like you already have lots of additional variables to play with! good luck!, have fun.
Everything except those orange tulips was tank developed in c41 unicolor chemistry warm or at room temp in a garage in spring/winter.
https://www.flickr.com/search/?user_...all=1&text=c41
process info:
Developing E3 E4 Ektachrome slide films in C41:
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