@jeffpa, you can also get a feel for what will happen if you do that just by playing around in Target. For example, if you go to a more occlusive fit (power domes), Spheric noise reduction won’t have to work as hard (not sure why). But with an occlusive fit like power domes, slim tips or cShells (either with no vent), the “effort” put in by Spheric speech clarity for Spheric Speech in Loud Noise is only 5 (as shown below). Whereas for any open fit, Spheric Speech Clarity jumps up to the max rating of 7. Maybe with an open fit and some noise leaking directly to your eardrums, Spheric Speech tries to remove even more noise from the processed sound to compensate? Since I have decent low-frequency hearing, more noise would leak directly to my eardrums and be heard if I wear an open fit.
(above with my audiogram and an occlusive fit).
If you make the dome change, you should also run feedback testing again, as the results of the feedback testing are used to decide how open your fit really is and, IIRC, something about the acoustic parameters of your ear canal with your new receiver configuration. That could affect the intensity at which Target determines Spheric Speech Clarity should be applied by default.
You can also look at how the change in the openness of your fit will change your fitting curves, what happens if you turn on occlusion compensation, etc. Lots of ways to fritter away time testing! 
Footnote: The oddball thought occurred that Spheric Speech Clarity jumps up in the open fit situation as the receiver engages in active noise cancellation in the ear canal as well as digital signal processing. But if that were so, I think we would have heard about it from Target. So, it’s just an off-the-wall thought.