Drive strength is at some DC test condition, like 10% of
rail. Your peak current is found elsewhere, where the output
is more near midrail or higher. How the two relate has also
to do with the output slew rate and internal gate drive, a
slew rate limited buffer with exactly the same DC drive
strength will give you a very different peak value when
the load capacitance is small.
Max output frequency rating is the minimum value of the
frequency that will give good (and this itself is subject
to some judgment-call) swing at worst, worst, worst
P,V,T. If it's "almost good enough" in a nominal sim
you should expect 2-5X worse, somewhere (hot, slow,
low voltage is a good place to start). And remember
that internal supply - ground voltage droops below pin
voltage difference just when you need it to hang
tough for timing, so pad it some more.