That is correct. I'm measuring scrolling at low to medium speeds, where the majority of the text hasn't changed (this also corresponds to most editing tasks). I don't want to make the claim that I'm keeping up when scrolling at very high speeds. I think my assumptions are reasonable for an editor, but for a terminal scrolling at high speed is much more common. I have certainly considered fast-pathing monospaced font rendering (it would certainly be easy in the current architecture, and in fact we're doing that for the gutter numbers), but it hasn't seemed absolutely necessary, and going forward I want to make sure that rich text and i18n aren't treated as second class wrt code.