That last sentence is important ;) As there are a lot of users sending out Rising Start emails, so you may be spot on that people just skip opening them. I open all emails personally, I just don't vote them all.
But again, that's why I added 250 to 500 is a safer bet. And this is up to each person to decide for themselves, looking at their stats. In your case, I'd surely up that with at least 250. If you want to play even safer, 500. So that I totally agree on :)