I've not gone to P_12 yet, but running 'branched' and 'progressive' together by accident usually chokes my PPro_11 Superfly. YMMV...

Um, losing that top-end HDRI support seems unfortunate if you want to build a complex scene by stacking rendered 'cels'...

For taming HDRIs to manageable resolutions, you could try free Irfan View. Just give it time...