I jumped from a futaba 9451 .10 and 140oz to a Ace 1015 and OMG the difference is insane!
I now run the futaba in my CORR truck and it's more than enough, that servo you got should be ok for the buggy just won't have the torque in corners but you will sure be very responsive and quick in a straight line.
I had a Hitec HS-645 in my CRT.5 and found it a bit slow.
I've put a HS-7940TH in my new build and love the speed but I wonder about the quality. See this youtube vid of the brand new servo for the audio of the crunchy gears... http://www.youtube.com/watch?v=KEkhzjwSnXw