Speed of Vallon  

They may not squish or block eachother on the buff window, but you can only benefit from type I haste (incl. all spell hastes) from one buff. Even lower level chanter hastes stack with this icon, but the percentages won't stack. One spell plus one item to a max of 100%. I'd comment on bard songs, but they seem to be more complicated and there is less certainty about how they work. Different sites say different things on that topic.