I think the speed in Grip is fine. Honestly the game "feels" faster than many other games "look", because we have to deal with actual, punishing physics. Loosing control of the car because of excessive speed is actually a thing in Grip, where it isn't in other games. Driving on the razor edge of controlability is what gives the greatest "feeling" of speed, not just the absolute velocity.
It's why WRC feels faster than NASCAR, even though rally cars travel half as fast.