I did a lot of testing some time ago, and you really need to find out if your shooting style allows this to matter.
The raw, one-burst difference is not large from the slow cards to the fast; I don't have the numbers handy but from 30mbs to the fastest card maybe 20 vs. 30 shots. Now that can be significant for some, but 20 is 5 seconds at full speed, and for a lot of people they never get close to that.
To me the far bigger matter is... well, bigger. The files are so large, I now only shoot with 64G cards in the camera, so I can get through an entire event on one card. ANd you can buy two 64G cards of moderate speed for the price of one 32G card of absolute top speed (or last time I checked).
The other matter to consider is if you plan to use SD's as backup -- if you do, write speed is the SUM of the two card speeds, so you need to get very fast cards from both if you really want long bursts. As well as big cards.
I run with a slowish 128G backup SD card and a moderate speed 64G CF card. I very rarely hit the buffer full. It does happen.
So think hard before you decide you really need a super fast card. Or maybe you buy a small 1000x for only those few times, and most times use big moderate speed cards, and save a lot of money vs. all very fast cards.