I have been running a Hpi Apache C1 buggy recently and absolutely love it.
The stock electrics seem to be adequate for 4 cell use,although i have dropped the HPi 2200kv Flux Tork motor and Blur ESC into it from a HPi SC Super 5 or Vorza(6 cell capable),
i have just ordered a 19T pinion for 4 cell use at our track to give a bit more top speed but am intending to make it "truggy" D8T width and run it on 5 cells with 15T or 16T.
Great buggy,very impressed