You have to be careful when comparing other cameras and other stacking software.
Certainly when to stop (if at all) the stacking is a personal choice but there are other variables at play.
In the case of the LodeStar X2 it using a substantially more sensitive sensor than the 224 so there's more data in each of the initial exposures which makes the initial stacks look a little better (so the stack looks better with fewer exposures but there may be more noise present). Then there are the algorithms being used by the stacking software. High dynamic range (HDR) stacking really helps the sensitive sensor by not blowing out the brighter parts of an object, this allows for more aggressive histogram adjustment (allowing for more faint detail to be brought out). This difference makes it difficult to directly compare images from the different cameras.
With the variety of software options available we now have to ask a lot of questions about how an image was created to understand what we are seeing and how that would compare with something we are more familiar with.
Speaking of questions ... Martin, how did you take those really nice 7331 images?