Triple T bites up very well, you pretty much know you wont be on a fresh tire before even going, so to have a month old and 2 month old set is a good start. Carrying a 3 month old wouldnt hurt either. Ive also known at times even older tires were needed.
Southern id bring a fresh set with me, along with older sets.
I wouldnt worry about duro as much as amount of internal and age of tire. You can have a fresh set with a duro of 50, and a 2 month old set with a duro of 50, but they are much completely different tires on track.
Amount of internal will depend on what classes and whos prep you decide to use.