On the change in look, I think this is due to the Auto Adjustment being enabled - your background has changed, so the exposure and white balance changes, making the objects look different due to tone mapping even though the reflections etc. are the same. Try turning off Auto Adjustment and see if then the objects look the same. I think this is amplified because the direct visibility is a JPG with only SDR range, and the environment an HDRI, and an HDRI can have brightness way above what a JPG SDR image can have, thus making the Auto Adjustment make some pretty big changes to Exposure and White Balance.