Need help with buggy conversion

[glassdoctor]

Sounds to me like the 8XL would be a good choice. Sometimes we tend to over-analyze things. To a great extent, gearing can equalize the differences between a 7XL and 8XL. Everything is a trade-off... and like you said, a motor can't both have longer runtimes and draw more current at the same time, compared to another one.

Based on your need for speed I would say skip the 9XL.

The 7 or 8 is a toss up... I know hte 8 will have to be geared pretty high to get up to 45mph. My 1900kv motor clocks 45mph on when geared 18/46 on 4s packs. It's stupid fast even though the gearing sounds way tall. But there is a limit to how big a pinion you can put on there.

That's why I would leave the 7XL as an option if you really want to do 45mph on 4s.

So... 7 or 8? Both can be stupid fast with the proper pinion.

I would suggest putting a good 40mm fan on the esc and either a fan or heatsink on the motor.