I love this shoe. Great fit, very sticky rubber, and very durable. I climbed up to 5.11- minus before I busted through them and got a different pair. They're resoleable though so even after you move beyond them in skill level, they're great to have around.
I personally wear 2 sizes under my street shoe size in every La Sportiva climbing shoe I've bought. This is definitely something you should try on before buying (but keep in mind that they are leather and will stretch). A climbing shoe should fit like a glove (but doesn't need to be painfully tight) and while these shoes are amazing, finding a shoe that fits your foot shape is really the most important factor when buying a climbing shoe.