Having just spent 8 days cycling 1000 miles around Wales I did and would continue to just feather the brakes.
Assuming the new limit will be for B roads and country lanes and not A roads then 20mph will do, what with the hit and miss road surfaces and blind corners.
The new limit will not be for B roads and country lanes.
Where the default limit is currently 30mph (which are those officially called "restricted roads" - defined by having street lights), the defauilt limit will be 20mph from 17th September.
There will be exceptions to this, where the limit will remain 30 - by traffic order. And there will be some roads which do not have streetlights, that will be restricted to 20 by traffic order.
The map I linked to above shows all affected roads, both before and after the new laws and orders come in.
It is mainly (but not entirely) residential roads and shopping streets which will be 20.