That sounds good!
Is this how you are connecting the additional 2 packs?
Add 2 x 1300 packs in parallel to the stock 4480 pack means your total capacity becomes 7080mAh or 7.080 Ah
A 10C discharge rate means you theoretically may draw 70.80Amps continuous without ruining your batteries.
The Log files from the DJI Pilot app, with extension .TXT logs the Amps (after converting to csv here
DJI Log Converter) indicates the max amp draw on a stock P3P is around 18 Amps when climbing vertically (that's where you draw the max Amps) as can be seen on a screenshot in Dashware (unfortunately
HealthyDrones.com - Innovative flight data analysis that matters only shows cell voltage variance. Hope they will include Amps some time).
All that to say even 10c 4S 1300mAh packs should be more than enough.
But it would be great if someone with the battery mod posts their logged txt file to check the max amp draw .