I wouldn't be shocked at all if the number was between 5-10%. That's the ball park figure I have seen most often over the years although obviously nobody really knows.
In all honesty aside from the new/lower ranked fighters who should obviously be seeing a little more money, I agree with the pay system implemented by the UFC. Think about it in the majority of major sports which are commercially valuable, the general consensus is that our athletes are overpaid. I'm sure the majority of people have listened to their fair share of resentful comments on the subject from a fair number. God knows I have. And in all honesty I've more than likely been guilty of one or two myself.
I've also heard an argument that it is the pay scale and related issues could be one of the things that may hold the UFC and as a consequence MMA in general, back from developing and seriously becoming a threat to the status-quo of world sports. And I'm not sure that to me personally that would be a bad thing, speaking from a strictly selfish standpoint.
What I mean is that for me at least there was something to the fact that years ago barely anybody else I knew, knew what the UFC or MMA was. To me it felt like myself and the few people I knew who were into it, were onto something that spoke to us and that the majority could not understand. I'm not crazy, well at least not anymore. I'm happy that people who are putting their health on the line are being better compensated and that governments are no longer trying to wipe the sport from the face of the earth.
At the same time though maybe it was that uncertainty that gave the UFC its edge. The fact that for a good long while the future was very much uncertain, to me gave it an almost enjoy it while it lasts attitude. With mainstream acceptance came a complete change of feel. Obviously this was necessary for the future of the sport but what can I say. I'm stubborn and not too fond of change so that does not stop me from missing the old days.