Since you aren't taking this to the track I'm curious as to why you would be interested in the performance package other than the name or brake upgrades? Unless, of course, it's to get around the potholes in WI! All Mustangs are limited slip so it makes little difference if it's 3.31, 2.73, 3.55, etc. I'm in the same boat as hogasswild, there will be little difference on the street, besides the looks, in the package if you have little plans of utilizing the brake and suspension upgrades. Just my opinion of course but sounds like you would be better served saving your money until you drive the base for awhile and then get an idea of what you would really like.
2011 Shelby Convertible w/SVT Performance & Electronics Packages
2011 Shelby GTS V6 Convertible, AT, CAI, Aluminum DS, 3.73, Tune