A lot can depend on the punters that turn up. Some days can be more manic than others due to the date, weekday or weekend and if there is a race meet coming up.
This can also have an effect on the average lap times of any given group.
The length an width of the circuit is a big factor IMHO. Silverstone GP is capable of swallowing 70 bikes in one session thats, less bikes per mile than 40 at say mallory, but it does depend on so many aother variables, e.g how the bikes are released on to the circuit, the type of punters, and so on.
I seem to remember this sort of debate before about the Silverstone GP circuit.
If you really wanna have day a where you can call the shots just hire the whole circuit yerself!!
Better still do what Klaus Zwart did buy/build yer own.
Ray