I've been taking my Salsa Casserole for 22 miles each way on my commute. My fastest time has been 1:10 when the wind was perfect, my worst time has been 1:40.

My commute is half on the MUP, and half on a back highway including a segment that runs through a wildlife reserve.

IMO if you're going further than 5 miles fixed > singlespeed my legs need the slack.