Okay guys, from what I can see, this last problem of mine as expected was my fault - turns out, the size of the Reflection Sphere wasn’t totally covering my scene! DUH!
Somehow it had got scaled down to just a little bit larger than the widget icon itself (~60 for the radius); once I increased it to cover the scene, my metal objects started looking correct again! (I ended up pulling out the sphere and going with a reflection box since it better matched the scene anyway.)
http://www.willbelljr.net/public/unreal/CorrectedReflectionSphere.jpg
This worked correctly with a totally new and empty map; I even pulled out the animated sky and all the lights (totally black background) and with a single bulb, the metals looked good. I eventually added back in the orange sky seen in my test scene above.
In my quest to see if I could get from Allegorithmic to take a look at my problem here, I discovered that someone over on their forums was having the same issue](Adobe Support Community). Another good tidbit of information on import / export configuration was Here](https://support.allegorithmic.com/documentation/display/SPDOC/Unreal+Engine+4).
Hopefully this will help if anyone also stumbles across this issue in the future and looks for help…
The reflection probe HAS TO cover all the (metal) objects in you scene if you want them to look correct - just seeing that mirror ball in the viewport and thinking that is enough (like I did) will have you scratching your head like I was. You have to make sure it’s covering the scene!
My textures work fine as exported when everything is simply connected in the material setup - as I would have expected for a PBR material.
So what I was taught here earlier in this thread about the SRGB / Linear Color or Grayscale settings were correct after all, it was my not paying attention to the Reflection Sphere settings that got me in trouble again with my additional testing - LESSON LEARNED!