Ligatures are affecting scroll performance

I am using the FiraCode font with macligatures set. When scrolling down, MacVim seems to hiccup a bit, but when I scroll up it is very smooth. When I do not set macligatures it scrolls fine (but doesn't show the cool characters). I am testing the scroll speed using both my touchpad and jk keys and my key repeat is set at 1 which is 15ms.

This was originally posted in FiraCode's issues, but the solution to the problem probably lies in improving macligatures support.

OSX 10.11, MacbookPro Retina

Followed the instructions to

set macligatures
set guifont=Fira\ Code:h12

Doing some dumb testing against Activity Monitor, it looks like the CPU load when I scroll down is much lower (~%60) than when I scroll up (150-200%), so the downscrolling seems to be inhibiting the scroll rather than taking on a huge CPU load and causing framerate hiccups.

Looking around for some possibly related topics:
Guy with the same issue (Scroll to Amadeus Demarzi)
thread related to listchars

Empieza reproduciendo el informe en MacVim en macOS con Fira Code, usando set macligatures y la configuración de guifont indicada; después compara el desplazamiento hacia arriba y hacia abajo con y sin ligaduras. Lee como contexto la issue enlazada de FiraCode y el hilo relacionado de listchars; se considera terminado cuando el desplazamiento ya no muestre la ralentización direccional informada al habilitar macligatures.