Are you talking about performance per $ ?
Barcelona might be better than the current Xeon for the price, but I don't think that it is better than Q6600
The price of Q6600 is between AMD Opteron 2346 HE and 2347 and those have 1.8GHz and 1.9GHz clock speed respectively.
We haven't saw any benchmark for Barcelona and Q6600 yet. Personally I don't think those Barcelona are going to beat Q6600, but we need to wait and see some benchmarks