That's the set up I would like to build next. I have'nt run 3s in a buggy yet but I can't imagine that it would'nt be competitive. I would post a question in the brushless section tiltled 3s/1512/1.5d in a buggy? and see if anyone else has comments on 3s buggies. You'll get more feedback in that section. Also, check out this calc.:

http://www.scriptasylum.com/rc_speed/index.html