Go with a roll bar, for 400 bucks you cant beat the stiffened chassis and the saftey aspect especially if your tracking it.
The whole idea of 80mph+ with a harness bar or even worse, nothing, is scary although I have heard of STi’s taking a few rolls at those speeds and seing minimal roof caveing.
I am looking for a roll bar/harness setup too not that it would ever see as much use as in zongs car.