What is the maximum processing speed of NIOS II?

speaking from a theoretical point of view the effective processing speed would be 6*185Mhz, where the processor would process 4 instruction for 24 clock cycles without pipelining with pipelining it'll process (or atleast start processing) 24 instructions..

but this is only if there are no jump instructions in the program. where as the processor will have to dump all the pipelined instructions before the jump and start over from the new set of instructions.

so the effective processing speed is dependent on your program aswell as the nios processor version. because some versions support instruction prediction for effective pipelining.