What is the difference between 9.5,10,10.5 and 12" converters and when are they used ? I am looking to change out my stock D5 with a good street/strip converter to match my combo and see that some are using a 10" and some are using 12". Also is a after market 12" converter the same as a restalled D5 or are they two different animals. Just trying to educate myself before making a purchase. Thanks,ikle.