Fpga speed

no.

It depends on what you are trying to achieve.

Todays FPGAs contain high speed serializer, that can transmit and receive data with multiple Gigabits per second. But that's probably not what you are after.

Maximum speed largely depends on the design; buffer-to-buffer switching speed is much higher than any useful logic implementation. So, the raw switching value does not say anything.

For typical designs, Altera has a paper that compares NIOS implementation across different devices. Maybe altera's nios ii performance benchmarks (http://www.altera.com/literature/ds/ds_nios2_perf.pdf) could be a start?

I am running significant processing up to and over 400 MHz with 128b datapath in SIVGT (highest speed grade). Not bad.

Jerry