I can't provide you with sound clips but I have heard drilled out pipes and offroad pipes at the same time. My friend has them drilled out and they sound better than stock, much better. But they do not quite match the sound provided by the offroads (I have them on my bike). If money isn't a problem I think it is a no question about it go for the offroads. If you want to save a buck or two then DIY your pipes, you won't be sorry. Of course I think the Toga pipes by Norman Hyde provide the sweetest sound for the Tbird but your mileage may varry.
Of course this is all my two cents worth of opinion

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Tom