I have given this question the benefit of considerable deep thought and the answer I have come to is this: somewhere between zero and -0.1! And that's looking on the optimistic side of things!
Lest you think me unduly cynical or so anti-European that I keep tripping over my prejudices, then I urge you to consider 'plucky little Poland'. The Poles, of course, are quite mad! Lest you doubt me, read the history of the Polish Lancers during Napoleon's time, and then their re-run in 1939 when their successors charged German tanks on horse-back - yeeeeees, quite! Anyway, the 'Euro-Polit-Bureau' has just re-appointed a previous Polish prime minister, Mr. Tusk, to the job of European Commissioner for a second term of office. They did this despite the fact that Mr. Tusk had been voted out of being Prime Minister of Poland by that dreadful collection of rubes usually referred to as 'the People'. The current Polish government, voted in by those self-same 'People', detest Mr. Trusk as being their very worst political enemy. (I know, I know, this is all a bit over-heated but, dammit, this is Poland!)
What the current Polish government failed to recognise is that Mr. Tusk, having already served one term as European Commissioner, is now regarded as 'un cher collègue' and therefor can do no wrong in the eyes of all the other 'chers collègues'. And if the current prime minister of Poland doesn't like it then as far as they are concerned he can take a jump in the Vistula!
I mention all this merely as background to ensure that you know the nature of the game when the Euro-fanatics are forced to deal with someone, anyone, who is not on the great Euro bus. And that is despite the fact that, on the whole, Poland has not made that many European enemies in recent history. So now let us consider Britain. I would suggest that in all the great organs of power within the European apparat, you could count the friends of Britain on one hand and it is not just a re-action to our intention to Brexit, they never liked us, they detest our history and the fact that on the whole, by and large, we have done quite well for ourselves despite the occasional boo-boo.
The resentment runs deep and we should expect absolutely no favours during these so-called 'negotiations'. This should become very clear, very quickly and so I hope that 'St. Theresa of May' is ready to simply walk away at the right moment.