As you're not changing the wire gauge to optimize the (0.7Ω) resistance/coil count/wattage output... the single coil runs much hotter ("heat flux" value - 631 mW/mm2 - higher number is "warmer") and has a more rapid time-to-temperature ("heat capacity" value 67 mJ/K - lower number is "faster") than a dual parallel, at HF - 158 mW/mm2 / HC - 152mJ/K.
Click the first two hyperlinks below - read the latter while observing value changes in the former - to better understand what I'm talking about.