P.S. Sorry that I did not really answer the question.
AFAIK, f/1.2 is the fastest F mount lens.
You can get metered prisms for the Fs. In fact, they are much more common than the standard prisms. And they came in at least four different types that I can think of (Photomic, Photomic T, Photomic TN, and Photomic FTn). Some are interchangeable and some are not. But due to the fact that they were designed for obsolete batteries, you will have to do some modifications to make the meter work properly.