This card is being used to store the Linux OS on a Raspberry Pi micro-computer, possibly a rather specialised application. It worked first time. In this setting, it is very hard to judge read and write speeds precisely as there are so many other variables operating. While the 'Extreme' range is fast, the 45MB/s printed on the label is notional. This is the fourth SanDisk SD I have purchased over the course of three years, the others for DSLRs, and all have performed flawlessly. I judge this brand's reliability and speed to justify its top-end prices.