Shooboo, the 5D2 has an internal buffer which can hold up to 13 raw files before it has to write them out to the memory card. So continuous burst shooting is always available, up to a point, with even the slowest card on the planet. As individual files are cleared from the buffer so space is made available to cary on shooting. So if you only shoot short bursts, with gaps in between, or longer bursts with longer gaps then you may find you don't need a super fast card. What you need depends entirely on whether or not you ever fill the buffer and how fast you want to resume shooting once the buffer is filled. If you have a card that can clear files at one file per second then you can judge how soon you can resume shooting and how many shots you can get off before re-filling the buffer and having to wait again.
For a lot of people there is no need for a fast card at all, while shooting, although some seem to feel it is important to be able to download the card to computer as fast as possible and are happy to pay a big premium for that privelege. Personally I use 32GB Transcend 133X cards in my 5D2 and 7D and find them perfectly adequate, even when firing off bursts. I've had them for over 18 months and never had a problem.
I do use a 30MB/s Sandisk Extreme III in my 1D3 (got it as a freebie with my 50D) and don't find it offers any advantage since the odds of me ever filling the internal buffer are approximately nil.
You can find a table of CF card performance figures for the 5D2 here....
http://www.robgalbraith.com/bins/camera_multi_page.asp?cid=6007-9784
My card comes in at a lowly 11.4 MB/s, while a Sandisk Extreme III 30MB/s card comes in at around 22MB/s. Since I don't fill my 5D2 buffer I'm completely happy with that performance and have chosen to spend my money on capacity rather than speed.
YMMV