I suppose you could try 2.5 ish ohms.
It's a heat calc. Use V * V / R where V is the voltage (3.2 for most stock e-cigs, some are 3.7, 3.7 for
mods, 5 v for 5vPT or regulated
mod), and R is the atty ohms (resistance). This gives you watts of heat. There are other factors, like atty design, etc. But it mostly depends on that calc. It will get you in the ballpark.
5 volts at 3.0 ohms is 8.33333 watts (25 / 3). Usually fine. Other considerations are your power supply. What are you plugging the 5v PT into? You need 2.0 amps.