No need for K&N to test it, just go to a performance car forum and ask about it. At least in my experience, many individuals have put their cars on the dyno and seen the difference, my buddy being one of them.
Granted the K&N filter made a smaller difference than other latter mods he did to his corvette Z06, including headers, camshaft and programming, but the filter DID make a difference on the dyno for him and others in his circle. Performance spark plugs did NOT make a measurable difference to him (disregarding position changes in the plug).

Even without any performance improvement at all, it still makes economic sense to get the TRD filter if you plan on keeping the car for more than 3 or 4 regular filter changes or so...not to mention it is maintnence you can now do less often.

Tom