[Patrick]

XL motor's are big enough for truggy's, but a 9xl on 4s will have to be geared up a fair bit to do 45mph, since it won't rev that high, not saying it's not possible though.
The KB 1700kv on 8s in a truggy...yeah that'll make the nitro guy's cry, but the motor may self destruct at that rpm. Not sure what their rated to.
I run a quark, neu 1515 2.5d (1700kv) on 5s in my maxx and will be putting it in my truggy once it's finished. In my maxx I can gear it for theoretically 44mph (using the calculator, and it looks about that fast) and I don't need to worry about temps. It has enough torque to still wheel stand at about 2/3 full speed. Hardest thing about driving it is keeping the front wheels on the ground. I don't use that gearing for racing so I'm not sure how It'd go (I'd be more worried about the Quark that anything else).
If you want 45mph without worry about temps a neu and an MGM would be a good combo, and preferably 5s or more.
If you want to use a feigao, then maybe a 9xl on 5s, but be prepared to watch temps.