This seems to be a pretty old topic. But from scanning this you are correct with black boxes limiting what you can do.
Im a Senior Insurance Consultant and motor insurance is one i mainly deal with.
Best way to start your quotes its putting your voluntary excess at 0 and then increasing it if needed depending on the price. All comparison websites wil ask for a vol excess before you see what the compulsory excess is set by the insurer.
Youll sometimes see the price of the insurance drop by 50 pounds for example if you set the vol excess with an extra 250... so whats the point of applying it.
Named drivers are usually good and the better the occupation they have and how long theyve had a fulluk liecense will help.