I´ve just bought size 8 when i´m 9 and a half in street. Yes, one and a half size smaller!!!
I´ve just used it a couple of times doing boulder, and they worked great. Yes, it hurts, but no so much.
I know at least 3 people who wear it smaller (that´s why I bought it smaller)
I know some people recommend to buy them same size or even bigger, I just tell you my experience.
Oh, and notice that my intend of use is for boulder and sport climbing. I put them, climb and take them off asap.