Thanks for your response Nick!
I was referring to the "app_search.engine.total_fields.limit" setting, let me see if I can break it down:
Scenario 1:
100 fields (stored but not searched)
10 fields searched and used for relevance tuning
5 fields returned
Scenario 2:
800 fields (stored but not searched)
10 fields searched and used for relevance tuning
5 fields returned
I think the performance be about the same since I'm searching over the same amount of fields?
I'll try it out! Thanks for the tips, I'll keep them in mind 