I'm asking how large (by which specifically I mean diameter in light-years, though a rough estimate of the number of stars would be appreciated) can the main body of the spiral galaxy get.
I'm familiar with NGC 6872, but its size is from the tip of one of the two outstretched arms to the other; I'm not interested in this size, because of the shape. I'm instead wondering how big of a diameter a spiral galaxy a la the Milky Way or the Sombrero Galaxy (as in, a circular galaxy with no arms stretching noticeably beyond the edges of the disk) could be, within whatever physical limitations of galactic formation apply to spirals.
If its at all relevant I'm intending my galaxy to be an flocculent unbarred spiral. I want it to be as big as I can get while still being a spiral galaxy.