In this video Ghidorah takes Godzilla from ground level to the edge of space. He does this from about 0:19 to 0:32 which is 13 seconds. The edge of space apparently starts at 100 km.
100/13=7.692307692307692 km/s or Hypersonic+ Flight speed
If we assume cloud level:
This states that cumulonimbus clouds are 16000m above the ground. This is a reasonable assumption to make because these clouds are storm clouds. 16000/13=1230.769231m/s
Supersonic+ flight speed
Edit: this can be used to work out lifting strength as well
Ghidorah weighs 141,056 tons. This should be Metric as the Godzilla franchise typically uses metric measurements for weight. He also lifted the 99,634 metric ton Godzilla.
141,056+99634= 240,690 Metric tons of mass overall or 240,690,000 kilograms
The velocity for the accepted end is 1230.769231m/s therefore to find KE we need to do
0.5*240,690,000*(1230.769231^2)= 182,297,751,547,651.6 joules or High 7-C, Town Level
Force in Newton’s is equal to work done (AKA energy transferred) in joules divided by distance in metres
F=182,297,751,547,651.6/16000
F=11,393,609,471.72822 Newtons or 1,161,824,830.2683759 kilograms of force
Class G lifting strength