I have used columnal priorly and it does provide most of the functionality that you want apart from the breakpoints feature.
It is easy to use and is adaptive. In mobile screens the grids degrades to a stack so all the column contents are shown one under the other.
However for the intelligent adaption feature, as you have outlined in the breakpoints feature : I would very strongly recommend you to use the CSS 3 media queries directly because that is exactly what they are meant for and they are not difficult to use. The CSS frameworks which provide these features under the sheets utilize media queries only.
Taking a look at http://twitter.github.com/bootstrap/scaffolding.html#responsive , Bootstrap's fluid grid does provide some convenient shortcuts for setting css properties for specific screen sizes which are not present in columnal.
