Differences between generations detailed in this thread:
Iron Ninjas!! Battle of the 250s!
I don't know that that 17.5% would apply to; that sounds much higher than I'd have said. The new-gens are down 1 - 2 peak rwhp from the pre-gens, which is more like 7% or 8% at most. The new-gens have somewhat more torque in the midrange, and are down in the upper ranges. Less compression, more restrictive intake/exhaust.