Personally, I would rather get a larger card at a slightly slower speed (I'm currently using 32GB cards). I prefer fewer cards to keep up with, change out, and download after a shoot. There are those who prefer smaller cards, though, as theyre typically a bit less expensive, and for the whole "all your eggs in one basket" mentality that you lose more in the rare, but possible, event of a card failure or loss.
For non-critical shoots, I have no problem using Kingston cards (I have several elite pro 32GB 133x). I've never had any issues, but have heard enough complaints over the years that I only view them as a last choice if I'm shooting a wedding, or something (if you think you may need an extra card & can't afford another sandisk or lexar). If you have tons of cash laying around- by all means, though, go for the fastest card out there- especially if you have a reader that can make use of it. Offloading to your computer is where you're most likely to see the biggest difference. In shooting, I practically never notice any difference between my sandisk extreme (400x, 60 MB/s) & extreme pro (600x, 90 MB/s). Really the only time I notice any major slowdown is if you are shooting to BOTH cf & sd at the same time. You'll never get over 133x, no matter how fast a sd card you put in (more at http://jeffcable.blogspot.com/2012/06/why-you-should-not-put-sd-card-in-your.html
). As for video, either the extreme or pro (or similar Lexar cards) are plenty fast.