Initially, my reaction was your description purports to describe a very exact comparison, but an important parameter is whether you’re going to the same HCP for both brands and whether the HCP is equally experienced with both, does REM, etc. So, you answered that part, which was unanswered in your initial post.
As @Bimodal_user points out, you won’t get the maximum noise reduction effect with the Spheres (or any other hearing aid) wearing an open fit. Especially with your good low-frequency hearing, if you wear an open fit, noise will leak directly to your eardrums and NOT get processed by the HAs. Open fits are a big thing to avoid occlusion, have a natural sound, preserve directionality through a real pinna effect, etc., but they’re lousy for noise reduction by the HAs (don’t ask me how I know… 
).
Edit_Update: Theoretically, a hearing aid could do active noise cancellation (ANC), playing frequencies in reverse phase to match the noise and cancel out pressure changes in your ear canals. Apple Air Pods Pro and Air Pods 4 can use active noise cancellation but it takes a toll on battery runtime and is more complicated. DSP processing of the digitized sound wave within the HA chip is a lot more energy-efficient.