The Futaba 3305 would work fine and it's only about $30.
I'm not sure what Coreless is all about tbh.
I don't think you need anything super duper fast personally. The normal perceivable delay time is .20seconds or so. So if your servo moves that fast your brain can't pickup on the delay. Although faster will offer superior performance generally speaking, it's not necessary to spend that much IMO.
That's just me though.
Kyosho V-One RRR - JP Modified Mugen X12 - GQ Racing Tires - Futaba servos - KO Helios w/Spektrum Pro - Maxy's Fuel
Losi 8ight 2.0 RTR for fun times