Yes, Euro IV is the cleanest. But it is lacking in lubrication properties because of sulfur reduction. The whole reason to use the 2T OIL is because the diesel fuel now contains to low of a sulfur content which many of the older designed engines are designed to run on. The current Euro II is still not good for mechanical injection pumps.
2T OIL is an injector cleaner and using it every tank will keep your nozzles clean as well as your combustion chambers. It also reduces emissions so less carbon buildup in the combustion chambers and less soot.