If you put exhaust without power comander or other fuel manager, bike will run like shit. Trust me. You will be spending lots and lots of money.
When you upgrade something, it changes the fuel+air ration and than needs to be corected-tuned so the bike will run better.
Exhaust,powercomander,that has to go on dyno to be tuned properly,you are looking at least 1500 dolars, at least.
I had a friend here the he sold his bike recently, he went back to Honda Exhaust to make his bike quiet and gain the low and midrange power.
When you will have the money, get everything at once and instal it, tune it, and you will have some extra power, maybe 5 to 10 horse power.
2013 Suzuki Hayabusa Limited Edition
Gone, but not forgotten,
2008 Honda CBR1000RR