If you want to run the high data rate modes w/o an issue, I would cancel. It will be able to do stills and the less extreme video modes... but when recording at the highest modes it might not keep up. All it has to do is dip below a certain minimum threshold (the data rate of what you're trying to write) longer than the buffer can cover and then your recording stops w/ error. It might happen in the first/mid/last sectors of the card... but you just don't know (heck, may not happen at all, or perhaps it will wait until you need it that 'one' time).
Plus keep in mind the extra minimum speed benefits more than just the 'extreme' modes... the faster you can write to card and clear buffer, the better.
My opinion is I want to get a card that can meet the demands of the device 100% of the time. Bonus if it can match the specs of the device on the high end.
Also for those looking, the Cobalts just jumped in price so watch out (due to demand?).
B&H had them for 600 dollars apiece yesterday. A bit pricey!