closed chamber vs open chamber

Did you mill the snot out of your 906's or are you still on the fence?

You guessed it Im on the fence, I have a set of 906 heads with a nice valve job and bigger valves and correct springs. My machine shop will mill them including intake for $350. I need to learn a little more(new question). I am going to use them on my road racing dodge

I was considering Aerohead , I dnt live far, can pick them up, but they offer open chamber heads,
Will closed chamber make a big difference?
(this is ***** and giggles my 67 cuda 383 project is wear my extra cash is going)