There is no where, not in the client, or the wiki, that says the percent chance of getting an item from Kleptomancy opposed to the +5 gold it gives you. The best we can do is estimate.
Why? Why aren't we allowed to see the base percentages?
I understand why it might be a good idea to hide this so people don't try to abuse this system to get items they want. However, if professional teams really wanted to, they could just stick someone in a room for hours/days testing every combination if it was that impactful, so I really don't think it's that big of a deal.
And even if it is a big deal, why can't we know the base percentages, that's used in most situations that aren't special?