Roll center debate

[Vega V-6]

Just looking for ideas on what roll center specs some have been using on their full bodied cars. I seem to see numbers for the front at 3 to 4 inches, and rear at 7 or 8 inches. Have people been able to achieve that front roll center on their street cars? Guys running some of the big autocross events, what roll center have they achieved? I'm building a tube frame v6 turbo'd Vega and have found out why you don't use a drag chassis kit for a autocross car. To get the roll center, caster camber where it needs to be i needed to change alot about the chassis, tubing bends and all. Like several others, they have found out the Mustang ll front end design leaves alot to be desired. I still missed my numbers i was trying to get for the front roll center. after the fact i wanted to raise the car 1 inch and lost some a arm angles i was shooting for and now i have about a 12" roll center. Is that too high to expect any good results? Just hoping to pick some minds and get some opinions on this subject.