Nah like most cycle shoes Sidi fit one or two sizes smaller. I've used 49 and 50 in Sidi, so at a guess the 51 would be about right for you. There is a Sidi size chart somewhere online that you can print out and measure your foot against to check.
Edit: There you go http://www.sidi.com.au/sidi-size-ruler.pdf
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Nah like most cycle shoes Sidi fit one or two sizes smaller. I've used 49 and 50 in Sidi, so at a guess the 51 would be about right for you. There is a Sidi size chart somewhere online that you can print out and measure your foot against to check.
Edit: There you go http://www.sidi.com.au/sidi-size-ruler.pdf