Can be fine, can be horrific... it’s a lottery. I do it quite often. Once on the M5 prepare for roadwork hell. There is currently a 30 mph section for example. You ain’t getting to Plymouth in less than 6 hours currently imo. Took me well over 4 to get to Bridgwater in Somerset last week. Roads are horrible at this time of the year, but it is a weekend I guess.
Dont forget you have the m6 50 zone currently too. M60,56,a556 (new link road) to M6 is usually best these days.