>FWIW, I pitted my D600 with a SanDisk 95 Mbps card against a >friends with a Delkin 41 Mbps. I shot a 23-frame burst, and >it cleared the buffer in 17 seconds. He managed a 30-shot >burst, and it cleared in the same time.<<<< >
Then you should buy the cheaper card if the two cameras had the same image size, quality, and other settings.
What you need to do is put his card in your camera and compare to your card under the exact same conditions (probably a static subject from a TriPod) Because not just the file size but other camera settings can make a huge difference in write time.