I don't think "base clock speed" has been a well-defined quantity or officially published specification for a few generations now. It's really just the default/recommended PL1 (long term turbo power limit) value, and what clock speed that corresponds to will depend on the workload.

I think we can be absolutely certain that the benchmark results Intel highlights are not what you can expect to see while the chip is limited to running at a 28 watt TDP.