This book answers your question for almost a century prior. http://www.amazon.fr/v%C3%A9ritable-hi%C3%A9rarchie-sociale-lancienne-France/dp/2600039856

It is based on the first "capitation" of 1695, a tax paid per person based on their class. Not income or asset, but class. What does constitute a class? The fact that you are listed in it! It gives an idea of the "social hierarchy". Until the last minute, even the clergy almost got included. However the scale gives an idea of the distribution of wealth within society (each person is taxed according to their position). It has 22 classes and ranks within each (in total, 569 ranks). The tax evolved throughout the century so I don't know about the later one (this was an exceptional tax for exceptional times, so not a yearly one).

Of course it is impossible to exactly gauge people's assets because each class has different ranks and from the ones where there are documents or where you evaluate their assets, the taxation is not progressive at all, it seems a bit random within a class. That tax is neither an income tax as Vauban argued for at the time and again, with the authors' evaluation, the ratio greatly varies (for example, in the first class, the highest income (the count of Toulouse, bastard of Louis XIV) and the lowest one - General treasurer of the Navy, their respective income varies from 1 to 83 (1.5 million livres for the Count of Toulouse, 18K of the general treasurer). The count of Toulouse is in several categories at once, being taxed as himself, and also in the second class as a marshal (he was the admiral of France which is where his fabulous income comes from since he got a cut of wreckage spoils) - who actually didn't have to pay as such, but they were listed as 2nd class. So that is definitely not an exact scale to judge income.

The book gives the highest and the lowest documented income in each class (mostly the public income - ie, military, civil servant, etc.). The tax was not based on that income but on whether your position was listed in a class (which shows that some positions were more than just income). The top earner in the first class, as already mentioned was the count of Toulouse. The lowest of the 22nd was guard receiving board and food at the navy arsenal, with an income of 120 livres a year. Income disparity in the 22nd is not so big (1 to 1.5)

The 1st class had to pay 2000 livres, the 22nd only 1 livre.

This does not give a percentage of the wealth divide, but it gives you an idea of scale. A lowly guard (that receive food and boarding gratis), which was in the 22nd class as well as sheperds, waiters and such, had basically 120 livres a year of income. The most fabulously wealthy (the Bill Gates of the time) were earning 10,000 times that. Saint-Simon says in his memoirs, at the moment of the death of Monsieur (brother of Louis XIV), that his son, the duke of Orleans (future regent) inherited all his income. He thought that to be extravagant since he already got a lot, and I don't remember exactly but, he lists all the pensions and brings up the total, which is on par with what the count of Toulouse got, let's say 2 millions (1.8 IIRC). But those kind of income are literally a couple of people. The Prince de Conde, with the second income of the first class has 540,000 livres, three times less than the count of Toulouse. The top dukes are getting in the 100K's.

If we assume that waiters (whose income cannot be documented unlike the guard receiving board at the Navy Arsenal) got less than half of the latter's income, let's say 50 livres a year, and what the favorite son of Louis XIV got, we see a factor of 40,000. If we compare with the top princes and dukes, we get a factor of 2000

Now put that in perspective today. In the US, a waiter probably makes 25K a year. How much does the richest of the richest, the number #1 of of the 0.01%, make? If we keep the same income divide as under Louis XIV, we get 1 billions. It probably is what Bill Gates makes if we include all the tax trickery (those people don't have much personal earnings, they always have a company for everything). If we compare with the average dude of top classes (the dukes and peers, who were just a few dozens) who would be the social equivalent of some top Wall Street investment bankers, we would get 50 millions dollars...

I do believe that, if the difference between the #1 and the lowest of the low (in my example I took half of the lowest documented income) during Louis XIV's reign is probably on par with what we have now between Bill Gates and Jenny manning the drive-thru at a McDonalds in Nowhere, Indiana, I very much doubt that now there are only 50 people in the US earning more than 50 millions a year. So I would venture a guess that, the current US society, is more top heavy in income disparity than was Louis XIV's France.