TLET Route Planning

I've been giving a little thought today for our planned route for Tring-Land's End-Tring (TLET for short). We'll probably take a slightly different route back than there, and plan to stay with friends at Newbury and my brother and his wife in Penzance. I'm also trying to keep the daily mileages below 65 and avoid any major hills and dual carriageways - mainly for my wife's benefit, and bearing in mind we'll be carrying luggage. My first draft is as follows:

1. Tring to Newbury - 50 miles
2. Newbury to Shepton Mallet - 65 miles
3. Shepton Mallet to Crediton - 65 miles
4. Crediton to Liskeard  (north of Dartmoor) - 53 miles
5. Liskeard to Penzance - 63 miles
6. Penzance - Land's End - Penzance - 20 miles

We plan to have a day or two at Penzance before heading back home.