Using $response->setStatusCode(200, "OK"); (slows my response)

Hello guys,

I am running some AB tests against an API I am building... I noticed when I remove this command

$response->setStatusCode(200,  "OK");

My Requests Per Second go from 15-20 to 550-600 !! Anyone else experience that?

Btw, I setHeaders, I set a large Data set using $response->setJsonContent() etc to the response before i send $response->send(); But as soon as I add the setStatusCode line it goes to ****

If I use standard PHP header() it seems fine , still get 600 requests per second

header($_SERVER['SERVER_PROTOCOL']." 400 Bad Request");