As seen here at two minutes 34 seconds, Jem'Hadar "bug" moves about 5 its lenghts in 2 seconds. Its length appears to be 1/6th to 1/5th of Odissey's length, or 107 to 128 meters, with width of 115 to 138 meters, and height of 29 to 34.8 meters( 1 ), resulting in speed from 267 to 320 meters per second.
Now, mass. USS Voyager was stated to weight 700 000 metric tons at 344 meters. Width is 134 meters, and height 63.6 meters ( 1 2 ).
Volume of Jem'hadar's "box" is 356 845 to 614 707 cubic meters; actual volume of fighter is around 1/3 of that - that is, 118 948 to 204 902 m^3. Voyager's box volume is 2 931 706 cubic meters, with volume of ship being around 1/3rd of box, or 977 235 cubic meters.
We see that Voyager has larger volume, with factor being from 4.8 to 8.2. That gives weight of 85 366 to 145 833 metric tons for "bug"; resulting in KE of 3.043 x 10e12 to 7.467 x 10e12 J, or 0.73 to 1.7 kilotons.
Here we have asteroid with width of 44 meters and height of 66 meters impacting ISD's bridge at 500 m/s (values estimations are eyeballed but I don't think real values are off by too large margin).
Volume of asteroid should be 100 355 m^3 or 1.0355x10e11 cm^3; density should range between 2.2 and 7.7 grams per cubic centimeter. So mass is between 2.2x10e11 and 7.73x10e11 grams or 2.2x10e8 and 7.73x10e8 kilograms, which gives us value of 2.75x10e13 and 9.66x10e13 J (27.5 and 96.6 TJ). That is 6.57 and 23 kilotons. Bridge is completely obliterated, as seen in above screenshots.
It should be noted, however, that both are low end estimates. TESB asteroid hit bridge, which seems to be less armoured than main hull, while Jem'Hadar "bug" suffered warp core breach, as seen below; which might add anywhere from few hundred megatons to few gigatons to value.
