6502.org

My core synthesized for 100 MHz without effort, including internal memory and peripherals, on a Spartan 6. I didn't attempt to push it harder at the time.

But it depends a lot on the device and synthesis tools, and things attached to the core. So for a fair comparison it's best if you synthesize it yourself, using the same settings as for your own core.

You didn't add the peripherals and internal memory into source code on Github, did you?