Don't Be Fooled By Write Speed
Above you see the advertised specs for the CF cards I use in my Canon EOS 5Ds cameras.
That has absolutely no effect on how fast I can see the images I’m recording as I run around a hotel trying to capture some shots of every session going on at one time. “Why?”, you ask. Because the write speed of my cameras is right around 100 MB/s, depending on the detail included in the image. It will run between 99 and 101 MB/s. So that’s as fast as the images can be transferred from card to camera regardless of the potential write speed of the card.
The last time I looked, the specs for cameras available through retail outlets didn’t include the write speed of the camera. I'd guess that the folks writing those specs don't expect you to be looking for that particular number.
The speed of your card may very well improve the speed of downloading from your card to your computer or, as in my case, separate hard drive. That will depend on the card reader, the connections used, and your computer.
I haven't looked into every camera from every manufacturer but, from my initial searching it seems that your average "high end" camera will transfer images to the card at around 100 MB/s regardless of the card.