Calc Gurren Lagann - Sayrune's underwater speed

Sayrune moves underwater at incredible speeds. Scaling Sayrune from Gurren Lagann. From my previous calc, Kamina is 184cm tall.
52 pixels = 184cm (1.84m)
1 pixel = 1.84m/52 = 0.0353846154m
0.0353846154m X 544 = 19.2492308m
0.0353846154m X 298 = 10.5446154m
0.0353846154m X 39 = 1.38m

Next, we scale Gurren Lagann's head to Sayrune.
87 pixels = 1.38m
1 pixel = 1.38m/87 = 0.015862069m
0.015862069m X 1598 = 25.3475863m
1598 + 112 + 97 + 692 + 244 + 1223 + 225 = 4191 pixels
0.015862069m X 4191 = 66.4779312m

Not sure if the tail would be visible above water or not, so we'll go with a low end of the main body and a high end of the full length.
Timeframe is 4 frames.

T = 1s/24
= 41.6666667ms X 4
= 0.166666667s

(Low end)
28 pixels = 25.3475863m
1 pixel = 25.3475863m/28 = 0.905270939m
0.905270939m X 442 = 400.129755m

T = 400.129755m/0.166666667s
= 2400.77853/340.29
= Mach 7.05509574

(High end)
28 pixels = 66.4779312m
1 pixel = 66.4779312m/28 = 2.37421183m
2.37421183m X 442 = 1049.40163m

T = 1049.40163m/0.166666667s
= 6296.40977/340.29
= Mach 18.5030702

Final Results
Sayrune's total length = 66.478m
Sayrune's underwater speed (low end) = Mach 7.055
Sayrune's underwater speed (high end) = Mach 18.503