Watts is watts?

[Serum]

You mix different things up.

Power isn't the same as capacity.

If you want the same capacity; (assuming you mean to achieve the same runtime) you can go with 60V 10Ah batteries or 6V 100Ah.
But i understand where you want to go;

I would prefer a 6S setup 3200 over a 4S 5000. Even though the 4S setup has got more stored energy. Most likely, assuming both motors on both setups run 30000 rpm at WOT (different KV motors) , the 6S setup will run cooler (more efficient)

You could play with the EPA on your transmitter and use a higher KV motor on a higher voltage and tame it down by limiting the throttle to lets say 60 percent.