did you feel that the starting punch is good but the middle range acceration is slower than brush motor? I always reach the top speed at the very end of the straight! (I run 6.5r , the 8 mins. race result just similar to my 10turn.)

I run pro4 with 8.3 gear ratio 64 pitch gear.(if I run 8.5-8.7 will be too slow)
can I use 48 pitch gear to strengthen the middle range acceration ?

I found that a lot of the feel is based on gearing. I had to gear way down with the hotter motor to get the punch back. The top end was about the same and I ran about 9 minutes in 12th with a 5.5 motor.

From what I've seen the 48 pitch gears will make the problem worse because there's a bigger change between the ratio for every tooth on the pinion. For the most part, the same ratio will give the same performance regardless of the gear pitch.

I think the 6.5 will run similar to a 10 turn (but have a different feel). In 12th the 5.5 turn runs similar to a 9 turn brushed but needs a tooth or two less gear.