If you get two 5s1p 4000 packs. You will need to wired them in parrellal.
If you get a 3s2p and 2s 2p 8000 mah packs wired in series.
Both have same volts and mah rating.
Do you have a charger to charge 5s lipos?

Ok it´s starting to make sence :-)

Yes my charger can take 1-5 lipo cells (3,6 to 18,5 volts)

Thanks a lot