When does a non Precision slic become a restriction?

[Turbo6Smackdown]

When my non Precision 23 row slic become a restriction? I know about this slic going tens already, but I was more interested in when it starts to slow the airflow down, not totally hold you back. Much like the stock air box set-up thread from last week. Even though it's been in the low tens, they had to make a lot more power to overcome that bottleneck. How do we determine if we're operating an inefficient combo? (besides just switching parts and doing back to back runs)