I'm no expert on this but I want to add this as well. The 77 series fipk is metal as opposed to the 57 which is plastic. Think heat... The metal one has been proven to have less HP gains than the 57. That also goes along with what Dingo said. I think the 77 series is little more than bling for the engine bay.
K&N can increase HP and Torque. They do provide dyno sheets for some vehicles. I had one on my colorado, which K&N provided a dyno result for. http://www.knfilters.com/dynocharts/57-3043_dyno.pdf
And my butt dyno noticed a difference too, lol.
Bottom line is with the right part, the 57 series, and the right combination of upgrades you can realize performance benefits from a fipk, just not on an edge, IMO.