In June, I checked out from Land's End to Bristol. I decided that the best routes through Penzance and Exeter were to avoid the bypasses. The route was definitely lumpy, but at least I would be quite fresh near the start.
Immediately following my schedule being circulated, I was advised that the Penzance decision was a bad one. In practice though, I would say that Penzance at 8:30 am on a Monday is about as busy as London at 1 am on a Sunday.