To throw another factor in - at the apex of the wingover his speed will be at a minimum and as the nose drops on the initial part of the recovery, he will accelerate. At some point as he starts to flare, the speed will start to reduce (or at least stop increasing) once the nose is level with the horizon, the speed will reduce (but not at such a rapid rate as when he hits the water).
Lots of variables in the 'easy' assessment of impact speed......
What you can say for sure is that the speed isn't a constant 90 kts from apex to impact.