What are the formulas to use when determing a brushless setup?

[Finnster]

I'd say there are good rules of thumb, rather than good rules.

Just like cars and hp/lb. You could do the same thing w/ watts/lb for BL cars.
20hp/lb is a normal commuter car. 10hp/lb is a fast car.

Say 170W/lb is good for 40mph. 2500w in a 10lb car is going to be really freaking fast.
Got a 20lb Baja? How does ~3500W sound for 40ish? 5000W is prolly a real fast baja.

I had 1200W+ in my CRT.5 when I was braking 60mph. This was ~280W/lb.