I'm not sure what the exact limit for getting the vote power slider is, but since a while ago, I personally invested a sizable sum into Steem Power, I can now vote quite liberally using only 5% of my voting power each time and still have a somewhat financially efficient vote without exhausting it right away.

The new users' vote is always at 100%, at least on Steemit, so it gets wasted quite fast. Although with that much steem power it doesn't really matter if it does.

I used to upvote almost everything, but these days I have a standard I try to uphold. You can read about it here and here.

In a nutshell I am very generous with my upvotes, but also try to keep my downvote strict but fair.