I think it would be good to link to the research Racing Beat has done on the subject:
http://www.racingbeat.com/Tech/Tech.Exhaust.2.htm
I'm not sure about the collected diameter you posted, though. That would indicate a collected diameter of 2.75" for a typical 2" primary setup, which is big. 2.5" OD is the largest I would go for a street-driven two-rotor, preferably 2.25" or even 2" depending on your porting and so forth.