Speed dependency is a very complicated question.
General theory and results from synthetic test can be very different from real life experience.
In real life speed depends on huge amount of factors. Its not only the energy loss of the rubber.
Its about the properties of the rubber-blade system, the dynamic of change of the parameters /usually non-linear, no matter how we feel it/ and the personal evaluation of the results, depending on players' style and preferences.
Some rubbers may be faster with max sponge and on stiffer blades, but not faster, or even slower on more vibrating and/or more flexy blades. And it will depend on the style too. Better top spin produce faster balls. Different players will feel differently with the different spin capabilities of thinner or thicker sponges.
Speed change, depending on the type and strength of the impact, is another factor. A thicker sponge of the same model may be more sringy with softer touches, or the opposite, and it may have faster "max" speed, or not, where "max" speed is very personal.
For me and my rubber-blade systems Xiom Omega V Asia and Tour do have greater max speed both with max thickness and softer touches, the Tour being sensibly more springy with max sponge on softer touches. Omega 7 Asia is more springy with max sponge on softer touches, but the "max" speed is not faster than the 2.0 sponge, though for me definitely the max sponge is more spiny.
So - different rubbers on different blades and in the hands of different players would give different results.