Nick, "in it's day" are the important words here, and it's day was around the late 1950's and early 1960's, before Girling made it's calipers that were twice the size, which Bristol and many other performance car manufacturers adopted.
I agree that they will work better when everything is set up as per manufacturers spec, as most mechanical things will, but in reality brakes also have to work well in sub-optimal condition.
My experience with the Dunlop brakes were on an Aston DB4. I had the brakes rebuilt after I bought the car so they were in perfect condition. They were
adequate around town, but when I used the car in a rally (Classic Adelaide) they suffered badly from brake fade.
This is a widely reported problem with the Dunlop brakes which is no doubt why so many companies have developed replacement upgrades for them.
Incidentally, Bristol now offer brake "upgrades", so obviously they too believe there is room for improvement
