I am not aware of the details that you want to achieve but like others have said, a sofcore cannot run at very high frequency. The actual frequency depends on what version of core you choose (simple or complex) and what device you are using and what speed grade the device has.
I may add here that if anyone needs a high performance software execution on FPGA which will likely be complimented by hardware i.e FPGA programmable logic part (since why else would once choose an FPGA) then the ideal solution is to use an SoC device. This is where we get SoC FPGA of Altera/Intel and the Zynq from Xilinx. Here we have a hard ARM processor core (dual core) incorporated into the same FPGA alongside the programmable logic part.