I use parallel mechs everyday and usually use 24g or 26g ss wire. I like a quick ramp and a warm vape so I aim between .12-.2 on round wire builds. The thicker the gauge, the longer it takes to ramp up and cool down. At this minute I am pulling on a dual parallel 26g ss 3mm coils at .14 resistance.
So, as Beck said, you will have to experiment to see where your preferences are. I was trying to get an idea of how you vape in my question before. You'll have to work to find this out. Keeping your batteries CDR in the forefront, use a calculator to construct a simple build that puts you in your 35-40w range. Throw it on a regulated and see how it vapes at say 3.7 to 4 volts.
EDIT:
Not sure if you plan on doing the maths yourself or using a calculator.
If you use an ohms calculator, you enter two values.
Enter the voltage and resistance and it will
Show you the amps drawn and wattage.