Can't comment on Sidi boots (I wear Alpinestars), but I have three pairs of Sidi cycling shoes and they are superb - really good quality and very comfortable - be aware that Sidis tend to fit quite narrow, only a problem if you have big plates of meat though!
They do squeak when walking them, those plastic "vertebrae" over the heels are the culprits. I've used a tiny amount of vaseline to make them less noisy :sigh
Other than that, no complaints here. They're a tight but comfortable fit.