I'm guilty of overcommenting on this page, so I'll take a break from straight line performance metrics and jump right to the lap times! ;D
https://docs.google.com/spreadsheets/d/1U2PVjLqTUjpSK21tb_NUXkTaqdy0qTsYJg_Dd9ME-fI/edit#gid=0
I made this spreadsheet widely readable for all petrolhead audiences; this means I have the Mustang counter on the right of the three pony car counters as well as on the bottom.
Usually the Mustang doesn't corner as well, but the Handling Pack GT500 is as expensive as a fully loaded ZL1 1LE. The CFTP GT500 however is as expensive as a fully loaded Redeye Widebody, so that explains the performance differences. Averaging best CFTP and best Handling Pack times, 7:15-7:16 around the 'ring is reasonable (ZL1 1LE is estimated at 1 sec slower than GM's verified test time, @7:17).
Contrary to its size and straight-line performance, it shouldn't lap more than 2 seconds behind the McLaren 600LT and Porsche 911 Turbo S because of its amazing set of 305- and 315-wide front and rear track tires.