If you use 250W+ PL2 mode, you can probably get more cores than 2 boosted that high, I would think.
So, the 5.3 GHz boost (and 4.9GHz all-core boost) is only under something called Turbo Velocity Boost.
This can only kick in when the CPU is below 70 degrees (50 degrees for mobile). It's not related to PL2 or anything, but instead, purely based on temperatures.
Now, while this is possible for ST workloads (but dear god that thermal density will not be kind, we're talking like 30W+ - probably more - for that single core), imagine how possible the 4.9GHz all-core stock turbo will be, given the 262W PL2 that needs to be dissipated. Not quite something I'd personally want to use.