Well I've got like 4 boxes of originals just sitting round collecting dust! I got a go go to use for stealth and my Darwin.and I think their at 2.5 ohm
2.5Ωs dual coil cartos exist but are not yet commonly found. I grabbed a few at vapefest in Vegas but have not tried them yet. While I am not 100% sure this is correct, I believe a dual coil carto with a 2.5Ω rating may have two 5Ωs coils in it (wired in parallel should read as 2.5Ωs). If yours fit on Darwin, Darwin will tell you what the Ωs rating is on first button press. If you have a multi-meter, you can test them before you put them on Darwin. To start, set Darwin at the soft-stop on the wheel (8.5 watts, some units this soft-stop may be at 8.4 or 8.6 but whatever yours is, use that as a starting place). Then adjust up/down slowly to taste. If they are dual coils, don't be surprised if they vape much cooler than regular 2.5Ωs cartos until you get to the upper range of the scale. However, do NOT start at the top of the scale just in case they are not dual coils. If you start at high watts, and they are single coils, you may get a burnt taste - could possibly burn some of the filler and then the carto will never really taste right. Just start mid-way and play from there.
While I am not a fan of dual coils, I do try the new ones occasionally. I have not found any that I like - yet. However, I find the EMDCC holds a lot of juice and has the best flavor (of all DCCs I have so far tried) for my juice - but only at higher watts settings on Darwin.
Hope this helps you.