XDA never sleeps, it seems. Popular developer Coolbho3000 over at the equally-popular phone developer forums has managed to create a custom kernel for the HTC EVO 4G that will allow users to overclock it to 1.26GHz. For now, he claims it’s stable, but your mileage is going to vary so proceed with caution.
What’s more is that he claims it could go even higher, but a bit more work needs to be done.
I got an EVO myself and managed to overclock it to 1.267GHz. We could probably go even higher, but that requires more extensive changes.
In the meantime, go peak your head inside that thread on XDA if you want to check this out for yourself.