In the Losi I would run the toughest servo you can get. I've heard the JR servos hold up well. I didn't have the best luck with Hi-tec as a throttle servo in my Losi, so I cant recommend that. However Hitec did work well in the steering though and they have great customer service. Save your hitec receipt so you can send it in if anything happens.
Here are some top models the fast guys are running:
For steering:
http://www.airlandhobbies.com/catalo...7380274541.htm
For Throttle:
http://www.airlandhobbies.com/catalo...7360258464.htm
I currently run these in my Xray XB808's:
Steering:
http://www.airlandhobbies.com/catalo...7350242047.htm
Throttle:
Futaba brushless Hi-speed BLS451