Go for a good FM radio for glitch protection. JR, Futaba, Hitec, KO Propo and Airtronics are the main players (i've probably forgotten a lot of other companies). I prefer Futaba, they make some good budget FM systems, have a look around.
What hop-ups have u got on your HPI? My Uncle has one, i had a drive of it a while ago, he has graphite shock towers, 2 speed (don't know if it comes stock???) lots of tires and a Novarossi engine