Really hard to say. I always wonder. If I look at @wang I would say 50%. And he has a bot voting for him. He plays the number. Lets say you vote at 100% each time so you wait 36m in between each vote and by chance you make the best possible upvote every time you have the best reward but reality is you,re going to have some miss. Better to cast let's say 4 votes. You end up 2 good one 2 bad one then it's the average that count and the chance are more in your favor that way. The more people will use their voting power the more the good post will tend to have close to the same payout. 

To have a better strategy go back through all your curation reward. Look at the 3-4 most paying one. Then study in what rank came your vote. That's mostly what will determine your curation reward and also you won't make money on curation unless you have a lot of SP. You shouldn't even bother much. Try to upvote great content with only 1-2 vote. But even then you would be better writing than curating. 

https://steemd.com/steemit/@teamsteem/the-ultimate-guide-to-steemit

On this page, click on advanced mode right next to the post’s title. Scroll down. Under the first white rectangle is written, vote detail. Click on it. Displayed are everyone who voted for you, in the order they voted. Rshares are related to the voter’s Steem Power they hold and their voting power which is explain above. Weight % is the % of the total reward each voters will be getting. You can only see it if no payout for this post haven’t been made yet. You can find the authors % of curation reward on the last line of the white rectangle. The line’s called author curate reward.