One Piece will over take Dragon Ball within 2 years just by sheer length. It will PROBABLY be the best selling manga of all time. Once it gets past Dragon Ball, I don't think that it will ever fall behind again. Kochikame MAY end up selling more than either, but that's a matter of whether or not it actually lasts so long that it can outsell One Piece, which should last for another 8-10 years, hopefully. Kochikame DOES have a pretty good chance of outselling Dragon Ball, but again, that's due to sheer volume. the series is over 160 volumes long, after all.
Naruto has a CHANCE of beating Slam Dunk, but that's it, and even that's a bit of a long shot. But either way, it's the 5th best selling Jump series in history, and that's something to be proud of. Then again, it may eventually feel a threat from JoJo's Bizarre Adventure, thanks again to sheer volume. That tends to help with volume sale numbers.