I would run a few gallons of the higher octane fuel, it will help keep deto under control.
Even though the SVT is tuned for 91 or higher when you start doing extended runs (20+ minutes at a whack) the heat generated during that time can most definitly cuase you to experience some deto (be it ever so light and you may not notice it) and the higher octane fuel should allow you to keep running the maximum spark advance (more power)
[B]1951 McCormick FARMALL M
2007 MINI Cooper S Turbo... new project car
1998 Chevy 3500 Ext cab, long bed, 4x4, duelly, turbo diesel
2004 Harley V-Rod.... sex on wheels
2011 Harley Electra Glide Ultra Limited