That is the thing, I'm not schooled on "ohms", I have been using the Vaporesso forz tank and the sub ohm coil is 0.4 Ohms. I'm sure the RDA coils are a different story.
If you've been liking the 0.4ohm drop-in coils and vaping at 50-60 watts...I'd get pre-wound coils that will allow you to continue that. For a
single coil RDA configuration you'd just buy 0.4ohm pre-wound coils and install 1 of them on the RDA. However, for a
dual coil configuration...you'd want to buy 0.8ohm coils, since you'll be using 2 coils.
Something else to consider is whether you want Kanthal A1 coils and/or SS316L coils. If you plan to use the Temperature Control function on your mod(s)...you'll need to get the SS316L coils. However, even if you
don't want to use the TC function...I'd still recommend going with the SS316L coils. IMO, and that of many others I know, we get a "cleaner" taste when using the SS316L coils. The taste also will somewhat depend on what wicking material used, too, though. Many people use wicking material that's Japanese Organic Cotton, and others use 100% rayon for it.
So, on FT, if you like the 0.4ohm resistance and your current wattage range...I'd search for Pre-wound or Pre-coiled SS316L 0.8ohm coils. They'll likely be available in packs of 50, 100, and/or 200. You might want to pay attention to the number of star ratings shown and the reviews for them. Some brands on FT have better ones of those than others.