I'm constantly surprised by how well our Malo keeps moving in very light air. While not suggesting she'd keep up with the Salonas of this world she still slips along quite nicely. The newer Malos/HRs/Najads etc, would I'm sure be even better.
The main difference is with very weak wind, like 2 to 4K, mostly thermic wind. With this wind your boat will be dead on the water while a performance cruiser if sailed upwind will make wind, going a bit faster than the wind.
Also with 8/10k, performance cruisers will be near their hull speed upwind while you will be going well, but not near hull speed. For that you will need 12 or 13K.
With more wind (+ 10) the differences are smaller, except when it blows at more than 15K and you are going downwind, than the differences starts to be big again.
But you are right, modern boats, even boats like the HR and Malo are much faster than older boats....but so are performance boats, compared with older performance boats