I don't know about the durability of the Sandstorm's driveline, or how others have handled adding power to them. I'd go with a kv rating of 3000 ~ 3800, or a 13.5T ~ 10.5T motor. Be ready to gear down as well when adding "more" motor to your RC. Something along the lines of ...
http://www.ebay.com/itm/SkyRC-Cheeta...0AAOSwOdpX1ujD, or something like...
http://www.rcmart.com/quicrun-brushl...Path=1560_1301 I don't think you really want to know what super low budget stuff I've used, and still using.