Being as vain as I am, the sound is worth a bit of popping and discomfort.
I know one person here tried to go vta without a recirculation cap, and that's bad news bears, you really gotta cap that s***. my car def doesnt go as smoothly with the greddy type s on vta. i did see a youtube video of a dsm with it in recirc who still retained the whistle, so I just ordered my fitting from SU. I know it won't be as loud, but if I get the great whistle I LOOOOOOVE with the driveability I want, it's a win-win situation