what you get via placeOrder() is rather what you get in tws in the preview window than what's in the contract description window. in general these two should be the same, though there might be cases when your current portfolio might affect the real margin requirement applied to your account. and that depends on many factors, product itself, account type, current portfolio etc... i don't even know the exact details. if you would want a generic margin requirement that is not related to your account, you would probably have to parse it from the details web page that ib provides from tws menu (the details menu item).
