Here's a trip report of a crossing made to Stornoway, complete with video clips.
Good service, and it is the shortest route. My own water crossings are limited to crossing the minch rather than the atlantic to get there, though.
On your fog question, the met office graph of "Low visibility events" is scaled 0-1 percent for Stornoway, and 0 to 7 percent for Wick. Looks like a clear win for Stornoway!