I’ve always shot weddings in JPG mode on my DSLRs, so buffer and write time was almost never an issue. Now with two Canon 5D Mark III’s and writing in RAW mode, the tiny 13 image buffer makes me worry I might miss a moment. Using all sorts of SD cards recently hasn’t improved the write speed, as I read online that the 5D’s SD card slot has a maximum of 133x, and not Ultra High Speed. The CF slot however, writes much faster. I did a quick test with my existing Lexar Professional 1000x SD card vs Transcend 400x CF. From the start of holding down the shutter in H mode to the end of all images being written, the SD card took 20.50 seconds, while the CF only took 14.26 seconds. Big improvement! Time to buy some new larger CF cards.
Update: I purchased new Lexar 1066x UDMA 7 CF cards, and the write speed for RAW files is no longer an issue as far as wedding action goes!