Most of the motors are listed as 2.25 to 2.75 HP, that's the peak power.
Below that is the continuous rating which is what you should concerned with, usually 1-2 HP.
You want one like this that has the fan, it's not built in but attached to the shaft.
NordicTrack Treadmill Drive Motor Windmill Generator | eBay
This is the type I used and it goes over 7000 rpm.
The ones you find that have a metal bracket attached generally don't come with a fan.
2.75 HP Nordic Track Treadmill Motor - Icon P/N M-147213 | eBay
I have one of these too and it also goes over 7000 rpm.