No he is right, in fifth they are absolutly flat at that sort of speed, your car is alot more "Peppy" as it's lighter, as he correctly says they respond much better at higher revs, I personally find them to be over geared for what they are, fifth at 5x MPH is something like 2,400RPM or less, good for economy etc but not good for response, I think thats partly the problem.

Martin