I most certainly could be wrong but this is what I've been told. Yes, they were commonly used in circle track originally but were also what Shelby put on the 427 side-oilers - according to some of the most informed the only single carb intakes used on the 427's from the factory. Some people then retrofited (mistake) their cars with dual quads.
The premise behind the offset carb is a dual plane intake that has relatively equal runner lengths. Essentially an effort to equalize the atomonization of the fuel/air mixture to each cylinder. A better description would be (because cirlce tracks have straights - most anyway
) a "race" intake with streetable manners - kind of the best of both worlds. Once again, I could be wrong but despite increases in technology I don't believe an performer rpm type intake achieves this - in fact, I believe it is simply a standard dual plane that promotes short runners and increased torque - like truck engines.
Someone with info. directly in the business might be able to shed more light on the topic.
Woodz428 - I know you have some "FE" goods up there but you state a Sidewinder should be about $450 - are you selling one? If you are I'm tempted to steal it for that!