[240 2NR]

Depends if they tested flywheel horsepower with or without the mechanical fan attached.  In anycase, the fan is a pretty substantial parasitic loss.   I know in first gear you can feel the disengagement during acceleration.  At the same time I think it will only engage in 1st and 2nd gear and only below certain speeds, so at freway speeds it's not an issue.  I believe Alex Chang had a write up for using only the electrical fan, and eliminating the mech one.  He claims to see little difference even in traffic in california between the water temps with the mech or small stock electric fan (but don't wuote me on it, I read his post several months ago, but he does detail how to wire this up).

As for the gerbil wheel comment, I think he was saying if the KA spun to around 8k, having a larger exhaust for a worthwhile top end would be meaningful.  Considering the power drop at 6k you're more likely to benefit from the top end, midrange and low end gains (or lack of loss) with a ~2.5," than to hope for any very minimal gains at only the "top end" with a 3" plus exhaust.