In the review section of this great website, Lee says the top speed of the 300E was 137. I think this is a little conservative, although I understand it is probably an average. I was going 135 (according to my speedometer) at about 5500-6000rpms and the car was still very SLOWLY accelerating.... Note: I was doing this on a track... not the road!
However, I was unable to push it further but it may have made it to 140 or better. I'll have to go back and try again!