score:4
If you're willing to accept a snapshot of British society in the later part of the period, then you can reference the table given here which was taken from A Treatise on the wealth, power and resources of the British Empire (1814).
While the data covers the whole of the British Empire (of the time), I would presume that the social stratification would be fairly uniform. So the percentage of rich to poor would be roughly the same for the British Isles as it would for the empire as a whole.
Taking the given definition of 'rich' being any free holder with a couple of staff, which would roughly correspond to the fifth class and above (I've ignored those in military service), we would get;
Rich - 4,316,110
Poor - 24,958,603
Which gives us an answer for 'rich' people of about 14% of the population.