If your blaster has 8500 rpm and 14/38 gearing with 20" tall tires here is your speed per gear.

1. 18.7 mph

2. 26.1 mph

3. 34.6 mph

4. 46.2 mph

5. 54.7 mph

6. 63.8 mph


Keep in mind this is at wide open throttle (8500rpm).

Sorry not able to calculate for a 250x.

thanks

Mike