I believe the best suited Dual Coil Carto would be a 2.5 ohm to ensure safe use with all juices, optimum flavor, TH, and vapor production. You really want to stay around that 9w-11w range for a vaping sweet spot. The 5v OMG comes off the charger at 5.2-5.3v the runs down to 4.7v-4.8v before needing a recharge. That translates to 11.23w - 8.83w using a 2.5 Ohm Cartomizer a perfect match.
A 2.0 ohm is still a little on the hot side and would run into issues still with some juices. A 3.0 Ohm, would really start to defeat the entire purpose of using a Dual Coil set-up and would simply be too cool. Resellers, manufacturers, and most experienced vapors would only recommend a 3.0 Ohm Dual Coil for high voltage mods like 6v or 7v application.
That information is readily available...a known known so to speak.
V4L just released a single coil 3.0 ohm DVCT which is really meant specifically for Passthrough use to lower current enough to work safely with their wall adapter and standard USB ports. If for whatever reason you find a 2.5 Dual Coil is juice safe, but still too warm for you a 3.0 ohm Single Coil would be viable back-up alternative.