The all-core max clock speed costs a lot of watts for that last 10% - close to 50% of total CPU consumption in some cases.

That's why undervolting has become a thing to do (unless you're an Intel CPU marketer) - give up a few percent of your all-core max clock rate and cut your wattage used by a lot.

I wonder then if the 9900X could be undervolted without losing more than a few percentage points of speed?