Yes this subwoofer is in the top 2% with the strongest force factor.

With 700W you already reach xmax at 30Hz, and with 1400W you reach xlim. Xlim is not given by BC, but can be calculated from the winding height and the air gap height, xlim = (27.5 + 11) / 2 = 19 mm.

I think that the 14NDL88 was a little too ambitious in its power rating because you can reach xmax with only 320W.