I cannot notice any delay at 100+ wpm, but one thing I had to get used to is typing key combinations faster/holding the key for the right duration, I still lift a bit too fast a few times per week, f.e. getting 'a instead of A, but it is definitely becoming second nature, and even if I cannot eliminate it completely the ergonomics of home row shift, and other handy dual function keys, makes it still totally worth it for me.
I wanted to use dual function keys, but as soon as there is one such key on the keyboard, I feel a delay for all the key presses. It is ok for the dual function key (the firmware needs to wait to decide a tap or hold), but not for all the other keys. So I avoid using this in my layouts.
Maybe this has changed recently? I have not tweaked my layout for about 6 months.