My understanding is that for a given OAT, aircraft weight and runway conditions, there is a minimum thrust level that will get you out of the airfield safely and should not matter whether it is achieved with derate and ATM or all ATM.
How does the EGT vary between these two options as this is the principal driver in terms of minimising damage to the engines?
Engine speed is also an issue. Can you confirm that when you say N1, is the unit RPM or %?
If it is the latter, does the datum 100% condition change with the derate level used?
Hope this helps.