At what level of performance does removing the plenum collar of Street Master's

[Qikbbstang]

and Street Dominators start working?  Has anyone "gutted" the plenum of a Holley Street Dominator or Ed Street Master on a stock to mild build and can advise on the before and after results?   We know from Jay's book "gutting the plenum" makes a substantial difference in a stout engine at WOT but I'm just wondering where that collar does work.
    Obviously both Holley and Edelbrock put the collars in the plenum for some reason(s) and of course Edelbrock advised and showed how to remove the plenum collar "for racing". I installed a stock Street Master years ago on a RV cam'd 351M w/ 500cfm Holley and right from off idle to top end the improvement was substantial all over the factory intake - it actually woke the truck up. I never would have believed an intake could feel so strong.  I'd already installed everything else and after 30,000 miles I scored a deal and put  the SM 400 intake on. Of course I'd never heard of gutting the plenum and kind of believe on my moderately tame build, cruising and towing etc it might have not done as well if I had.

[jayb]

I would say right around 400 horsepower.  The testing I did for my book showed a 10 HP improvement at that level, and bigger improvements at higher horsepower levels.  I think at 350 HP or below, it wouldn't make a difference, and might even hurt a little on the bottom end.