The limiting factor is not only the SD card, but also the data throughput on the memory in the camera. A full buffer gets by the collapse of the burst rate noticeable: suddenly no longer rattles the closure in high frequency but drops to one or two frames per second - at still depressed "continuous fire" on the trigger. Only when the buffer is written empty, the camera can work again with full burst rate.
My Nikon D610 writes with a maximum of 48 MB / s from the buffer to the card - and this card (with more than 60 MB / s read speed) allows 45 MB / s write speed. So do not brake quasi when the camera buffer must spend data as soon as possible in continuous shooting (sports). The 6% performance disadvantage (an image after 15 continuous shots) come with me not to wear - I never think as long as the shutter button depressed. The difference in price to the next speed class is, however, enormous. Therefore: Best Buy.