i agree they are too short, and am not keen on the guide making the lane change - however this fact means that the LC track pieces are passive and simple things, the same as standar non digital cross-overs, so shouldnt be too pricey...
As for the speeds - if they are the first piece after a curve, then a car will NOT have reached max speed; if they are the last piece before a curve, if the car is going flat out it will crash on the curve anyway!