My LHS told me with the 7700, you may need to buy a capacitor for your receiver and make sure the rest of your equipment (batteries, connectors, etc.) are top notch. The 7700 tends to draw a lot of current and sometimes will draw enough to drop the voltage which your receiver doesn't like to see. Spektrum sells a capacitor that you can plug into your receiver which has solved this problem with the 7700.
I ended up buying a 5700 because the owner of my LHS is a Tamiya fan and he didn't want to see my Evo IV end up getting wrecked because the setup was too fast. If I want to go faster, all I need to do is add some cells or get a 3S lipo.