In reply to RR:
Can't say exactly, but as a general rule of thumb for 5.10 climbing shoes. Get the size you'd buy your sneaker.
My feet are Eur 42 (in sneakers), my Quantums are 42, my Moccasyms are 42, my old Newtons were 42 and the old Arrowheads were 42... plus some other 5.10 I can't remember now, were also 42.
True, they are a bit different size. Quantums were the tightest fit. But they still work. I seem to recall that since 5.10 now have these lines of climbing shoes, the sizing reflects that. It has been also so in the past. So high performance (agressive) shoes will have a tighter fit than leisure all-day comfort shoes.
With Sportiva, the size are all over the place. Mythos 42, Miura VS 40.5, Python 40.5, Cobra 41 and Solution 41.5...