The raw interface speed is just a single parameter. In reality there are other factors like speed of flash memory chips, controller, latencies, speed of software, filesystem, speed of memory buffer in the camera. These all have impact how well the card plays with the camera, etc.
The fact that the signalling speed of the camera's card interface is limited doesn't mean that there can be no benefit of using a premium card that can write faster that the camera is capable of.
We are talking about cameras here. I don't really care about interface write speed. Sometimes I do care though about extra frames I can take in a burst or a few seconds faster time to next bust.
As I documented above, I can repeatedly measure the difference between 45mb/s and 90mb/s rated cards in my D600. The difference might not be significant for everybody, but still can be experienced as measurable improvement of buffer cleaning time or a number of frames captured over a period of time.