I can tell you straight away that 500m is a size you can ignore.
The Galor class is only 366m, and even a Vor'Cha class is only 480m. Clearly the Hideki should not be larger than either of these.
David Stipes estimates that the model had an on-screen size of around 150m, but I think you can take that with a pretty large pinch of salt as well considering its size was inconsistant between scenes in sacrifice of angels alone.
For a point of reference, the B'Rel class is 110m and I would have a hard time believing that the Hideki is larger than a B'Rel.
The DS9 technical manual says that its 85.7m in length, which is probably about the same size as the in-game runabouts. If you're going to prompt for the Hideki to be enlarged, then I would argue that that is the largest it should go to.