On a healthy stock 32, yeah pretty much, but not so much on 33-34s, those figures are from dyno testing done when designing those systems
As for gains depends on how bad the system you have is, if full stock with 20+ years of crap build up you could pick up a fair bit, but the biggest gains are dump-front-cat, then the rest depends on power level, the more power the bigger it needs to be
I designed my system to support 500awkws+ so overkill for most