I've found the same with my FA concentrates, I only need 3-6 % in any mix I do. To give an idea of how strong they are, I generally mix totally wicked concentrates at 20%, cos I like my flavours very strong.
Other FA concentrates I've used and liked are caramel, honey, irish cream and Vienna cream. Tried the tiramisu and coffee also, but didn't really like them much as stand alone flavours.