at very high RPM the full system makes a FEW more HP. a PC will give you more all around seat of the pants power. the stock system is hard to beat under MAX power at less than 8,000 rpm. others will say otherwise. the full system looks good, sounds good ,takes around 25 Lbs off the bike and makes maybe 4-5 more HP only at high RPM.
let the slamming start.
Another exhaust postwhere's the Popcorn.to slip-on,or not to slip-on...."8000rpm's and under it's hard to beat stock system",8000 RPM and over,you go to jail,or worse...Morgue..one of the few benefits of removing the Whole stock system...bike is 20lbs lighter...and so is your Wallet...when they make a slip-on for the gen 3 Z,with an exhaust valve,I will buy it,till then...
I'm pretty sure there's a zillion of these posts. Use the search.
Slip ons really don't do much for improving flow. You still retain the giant collector and cats which is the bulk of the resistance. They're there for sound only. Any performance gains to be had are minimal and you lose the use of the power valve reducing low RPM response.
Full systems get rid of all the crap, but be aware to get the best from them you'll need to re map.
As mentioned by notabiker and dr.nick, best gains are to be made from the reduced weight. With that said, a gym membership is cheaper than an exhaust...