I thought I would share an update on my problem.
It actually turned out that the Jetpack Photon CDN worked with my original code. However, it broke the responsive image update in WP4.4 – only delivering the original size image.
I haven’t been able to figure out a way to fix this but looking at the code on my start page (not using the ACF-plugin) it returns the image with a resize “value” and on the pages using ACF it returns with a fit “value”. Don’t know if this has anything to do with it but someone else might have an idea?