For under $150, the Feigaos are about it.

5S will be too much for the 7XL. I think it'll run really hot. For 5S, I wouldn't go much hotter than an 8XL for all out speed. For cooler running I'd go to the 9XL for 5S. Believe me, it will be insane.

Check out this thread...http://www.rc-monster.com/forum/showthread.php?t=7136

The video is of my 8ight T, which weighs around 10lbs running a 9XL on 4S lipo with a Quark monster Pro controller. With 5S it is just nuts. According to BrianG's speed calculator, I should be getting around 37mph as the truck is setup with 4S. On 5S, the calculator says that I'd be getting over 46mph with the 16/46 gearing that I was running.

Just keep in mind that it's always better to make more rpms with more voltage than just getting a higher kv motor.