on that journey, it's more of a "time of day" thing rather than which day - the possible delaying events may well be ok most of the day, with only transient issues at "peak" times. long term roadworks on the M5 J4 to J6 (smart motorway upgrade), around J12 (bridge works) and around Michaelwood Services (drainage works), all with 50mph and average speed cameras. you might get held up at J17 by traffic bound for Cribb's Causeway but otherwise M5 generally pain free.