Market for new mod. Difference between dual and single 18650s

So I'm in the market for a new mod to replace my boomstick 50w. I've been getting into twisted coils lately and the ramp up time for them is horrendous (i'm talking about 5+ second ramp ups), and it builds low without a ridiculous amount of wraps so I need a more powerful mod greater than 50 watts.

The main question is battery life. Does a dual 18650 mod like the Sig 150w TC have a better battery life than the IPV D2 at higher wattages? Those are the two mods I'm looking at now. I've read a lot of good reviews on the IPVD2, but a common negative is that battery life sucks at anything higher than 50ish watts. Would I get better in a 150w TC even though it's in series since I understand batteries configured in series doubles the amperage, but not the mAH. Or is it just the same as a single 18650 mod?

TL;DR: Does a dual 18650 mod in series have the same battery life as a single 18650 mod when using at higher (50+) watts?