Limit number of lines in find-file or execute-extended-command (M-x)

I am using fido-vertical (which in turn supposedly employs icomplete) and when I hit said key combinations there are like 20 suggestions displayed to start with. How can I limit this list to like 5 or sth. in the hope to make those command executions snappier?

I don't use fido, but I'd be awfully surprised if *displaying* the options was the slow part. Is it equally slow if you run `emacs -Q` and `M-x fido-vertical-mode`? If that's "snappy" and your regular config is not, then the problem presumably isn't the number of items being shown.

vanilla yields the same behavior, i.e. slight lag. Seems to be an issue with fido

Customize the icomplete group? There's a delay for large sets -- but it's only 0.15 seconds...