How fast is it? I haven't had a terminal that was as fast as xterm with a matrox millenium ii. That was 20 years ago which is pretty sad. Of course the terminals look better these days.
One of the first things I wrote was a terminal emulator using telnet to run on PC-DOS using a port of curses to connect to our Sun 3's. To think in 2017 people are still concerned about terminals is very surprising to me.
I don't know why it's slower when you make the window smaller, or when it's not being displayed. I expect the answer is "some kind of OpenGL bullshit" but beyond that...
gnome-terminal takes about 5 minutes to do this, but it has unlimited scrollback and as far as I can see alacritty has no scrollback whatsoever.
I'm guessing that "workstation" cards (designed for CAD etc.) may have moved on a bit since then, though.