There are tradeoffs to be made between executing more instructions per clock cycle and increasing the clock so measuring performance per clock can be interestin

There are tradeoffs to be made between executing more instructions per clock cycle and increasing the clock so measuring performance per clock can be interesting analytically but it doesn't actually say anything about how good a processor is overall. Even for a specific chip lowering it's clock speed will increase it's performance per clock as cache misses become less expensive.