Fastest for what?
Pure clock speed for a few threads is going to be the e3-1290 V2 at 3.7Ghz (4.1 Turbo). Although the 1290 is a pretty poor value for money. It's almost triple the cost of the e3 1270 V2 and only about 5% faster.
For huge throughput for pure number crunching on massive multi-threaded workloads it would be the E7-2870/4870/8870 with 10 2.4Ghz cores and 30MB of Cache and you'd want more than one.