SonicBoom is an open source Risc V core that is clock for clock competitive with the best from ARM. There is still the issue of matching clock speed and tweaking for a given process.
Foundries actually have an interest in helping to optimize an open core for their process as a selling point since it can be reused by multiple customers.
Their own paper[0] shows it performing at similar levels to the A72, a four year old core. Those are obviously really impressive results for an open source core.
Foundries actually have an interest in helping to optimize an open core for their process as a selling point since it can be reused by multiple customers.