i always run the cold side .25" larger since the air will get denser once it passes thru the intercooler. i match up my turbo compressor outlet with the hot side piping and match my throttle body to the cold side. on my last setup i had a 70mm (2.75") cold side with 2.75" cold side piping. my compressor outlet was 2.5", so i had a 2.5" hot side. if your hot side piping matches with the turbo outlet, it should be fine as long as you have hard pipes. you may want to bump up the cold side a tad if you are running more than stock psi and a upgraded intercooler. other than that, you most likely wont notice any gains