Chern,
As a practice, I would agree with you, however Matt has also ruled the opposite.
Speed 8 - Half speed due to Crippled = Speed 4. - 4 Speed Crit = parked.
The question is which speed reduction takes precident. If Crippling is first, the above applies, if the Speed Crit does, then you are speed 2. Since we have had 2 different answers for this, I would use the one that makes more sense, which IMHO is speed 2.
Dave