RE: Flattening, one formula to estimate the flattening coefficient (assuming uniform density and various other factors is:
Where w is (2 * PI / rotation period), r is mean radius and M is body mass (seconds, meters and kg). Oh, and G is the gravitational constant. This factor (f) can then be used to calculate the equatorial radius and polar radius as this:
Finally, you can compare this difference between the radii as a ratio of the equatorial radius. I've put this into a copy of the spreadsheet pasted earlier and sorted on this ratio. Results are promising:
Oblated Gas Giants
I'd say if you considered everything with a ratio of under 12, it'd be pretty close (or perhaps 10). Only 2 of the extreme ones are missed, and there's likely something else going on there (I think close binary orbits affect things, for example). Worth pointing out that the spreadsheet is (mostly) not journal data - journal data would help accuracy of calculations. I expect this would be quite a challenge to put in custom XML though, perhaps it's something Vithigar can build in (or maybe I could).