When I’m viewing a commit containing diffs with long lines, there is a fairly big performance slowdown: the scrolling becomes jagged, and CPU usage kicks up. This is only true when the long-line diffs are visible in the window (i.e. if I’m scrolling over other diffs in the same commit that have reasonable line lengths, then everything is smooth).
By long lines, I mean lines with ~100,000 columns. These files come about from scripted JSON output: unfortunate, but it would be nice if Sublime Merge could handle them.