There was a test floating around on SupraForums where they tested the actual filtration as well as power. HKS and Blitz were the 2 worst, filtering almost nothing. (White filter sheets after the filter were black). Apex'i and K&N were the cleanest.
Things may have changed, but I won't be using their filters anytime soon :\
Wouldn't mind seeing a revised 86-specific test along the same measures. Sure some vendor wants to win the gold medal and do it