Good question.

To date, street free agents have performed well above the expected average.

I once thought about stripping a team and starting all SFA at every position just to see what would the outcome be.

Having said all that, Mr. Cox has been sighted as saying he plans to reduce the effectiveness of said SFA in this coming update.

So, only he could really answer the question, because he is the only one who has any idea what the actual SFA performance scale will be from now on.

Good thing is once it's all ready to go, we can run the challenge game simulations and get an idea.