I'm wondering whether I should go for a faster card (e.g. SanDisk Extreme series) or can do just fine with slower card (e.g. SanDisk Ultra series) for use with Canon EOS 7D. I'm not planning to record any movies with it, though I like to take continuous shots (using bracketing, or for panning) in RAW+JPEG mode.
Thanks in advance.
If you don't plan to do video, you should be fine with the SanDisk Ultra series cards. Just keep in mind that the single RAW files by themselves can be from 25MB-33MB. So your cards will fill up fast, and you may need a higher speed card then you might have used in an older camera.
So there are two main reasons to get a faster memory card:
For each case, there is a maximum speed dictated by your equipment: the write speed of your camera when taking pictures, and the read speed of your reader (which could be your camera if you're using a USB cable to connect your camera to your computer) when retrieving the pictures. If you are comparing two cards and they are both slower than the maximum speed of your equipment, than buying the faster card will make a difference. If they're both faster than the maximum speed of your equipment, than buying the faster card will not make a difference.
I would suspect that the 7D is pretty fast, probably outpacing most memory cards, so you would notice a difference if you compared two cards to each other in your 7D, in a way that stressed the write speeds. On the other hand, if you don't stress your camera, you probably would never notice the difference.
So if you use burst mode a lot and use it to take more than just 3-5 pictures at a time, or you're always in a big hurry to get your pictures onto your computer, than you should get the faster card. If you only take a picture every few seconds or so, and you're patient and don't mind waiting a little longer to get your pictures, than there's no need to get the faster memory card. That said, I always get the fastest cards, even though I probably don't need them, because they're relatively cheap (compared to the cost of my camera and lenses), and because having the faster ones is just kinda cool.
Now the rest of this answer is actually completely irrelevant to your question, but it shows how I measured the effective write speed of different cards in my camera; I'm posting it in the hope that someone with a newer camera and a few different CF cards can repeat the experiment and provide some more up-to-date data:
I used a SanDisk Extreme III (2GB?) CF card, and two SD cards, a faster 4GB card and a slower 8GB card, with a CF-SD adapter. For each, I set my camera (a Canon 30D) to the largest file size (large JPG + RAW), set my camera to its fastest shutter speed (just trying to reduce the time spent with the shutter up as much as possible, so it didn't affect the experiment much; the most important thing with this experiment would be to be in Manual-everything mode so the camera doesn't spend more time thinking for one set of pictures than for another), and turned on the faster burst mode. Then I held down the shutter. I held the shutter down until the buffer filled up and the camera stopped taking pictures, and then I timed how long it took until the buffer reached '7' (the number that displays in the viewfinder indicating how many pictures can fit in the buffer). I'm not sure if these times are from when I first started taking pictures or when I stopped, but they are:
Basically I learned that CF cards are much faster than SD cards in an adapter (which shouldn't be a surprise), and that with that adapter a faster SD card did make a difference (which I wasn't really expecting).
It would be interesting to compare between different CF cards, to see how much of a difference that makes.
My take is that if you can afford the extra speed, get it. In the end result you may not need it, but you most assuredly can't suddenly get faster if you don't have it and do need it. In any event, the 7D is a fast shooter, so you may find having that extra speed is advantageous for burst shooting in raw as it will allow the camera to write to the card faster and become available for further shooting that much quicker.
