John, the only way you will gain any power from a free flow filter in the OE plumbing on a stock engine is if the original filter has inadequate flow. That seldom happens these days, outside of dirty filters, as most have more than enough. The overage is to account for restriction as the filter gets dirty.
Examples: I flow benched a factory Motorcraft air filter for my F150 two years ago. In the original air box, over several tests on a SuperFlow SF600 flow bench, it averaged 621.58 cfm... and it was a used filter with about 21K on it. A new, cleanable AEM Dryflow replacement element (a drop in like you are looking for) averaged 592.36 cfm but is reported to have 99.4+ percent efficient media(AEM makes no bones about this, BTW). We don't have the actual MC efficiency but most OEMs are in the 97-98+ percent area. And they are generally getting better with each passing year.
The big question, however, is how much air does the engine need? I know my 5.4L will want 420 cfm at 5500 rpm @ a calculated 80 percent volumetric efficiency. If I am generous and give it 85 percent VE, airflow goes up to 446 cfm. When was the last time my engine saw 5500 rpm? Never. Even though I have dyno'ed the truck extensively, and am running a custom tune, I keep the upper rpm limit at 5300. I never even see that rpm in my driving around as I am scratching to get every mpg. Max power is rated by Ford at 5000 rpm and the engine is pretty well done then. At 5000, the engine needs 405.8 cfm @ 85 % VE.
So, I have 621 cfm available from the stock, dirty filter. I need 405 to reach maximum power. How is more potential flow going to help? I have 53 percent more flow than I need.
You can increase power by changing the plumbing. That's highly variable because some aftermarket systems are better than others. You can tune them to achieve more power all thru the rpm range but the results are usually small with a stock engine. The plumbing changes are more a need when you increase power and airflow needs thru other tuning and need an intake system than can keep up. You might see a power increase by adding a freer flowing filter into the stock housing at that point.
Again, I can only refer back to my own tests. The full system on my truck, with all it's snorkels and silencers attached, flowed 621 cfm I made some mods to the stock system (the famous Gotts mod for F150s) and got it up to 637 cfm.
For comparison, a AEM Brute Force CAI system, which replaces all the OE stuff from the throttle body out, for the truck flowed 733.30 cfm. It knocked 6 degrees off the IAT and about 2/10s off 0-60 time. I couldn't see anything on the dyno (six runs) outside a margin for error, but it was trended upwards. The F-150s are hard to dyno and chassis dynos are notoriously hard to read small increases anyway. To get 2/10s on 0-60, there had to be something.
I got a little long-winded here but if you are looking for power, you won't find it (or much of it) by decreasing your filtering efficiency. Most OE or replacement filters deliver more than enough air, with a substantial reserve. Install a filter restriction gauge (Filter Minder) if you truck doesn't already have one, and replace the fitler when restriction reaches the OE specified limit or when the restriction increases 2.5 kPa (0.75" mercury) over the stock clean filter reading.
