trust those guys, without getting into too much depth, they are way smarter than the average joe, and generally speaking, the flow bench tells the whole truth, so if it flows better with those three OEM exaust valves, why would they put the others in there and hurt your performance when you paid them to make the head flow better? Most people just slap valves and other junk on a head and assume because it is aftermarket it will always make more power, but they fail to realize just how much engineering actually went into the stock parts to optimize them for the very head they are changing.

Cliffs: flow bench and knowledge FTW.