I have two models of Saucony shoe, and one is half size bigger than the other, so its not even consistent within their own brand.
Have a look on runningwarehouse.com and use the shoefitr application (the "show me how it fits" button). This is really useful - pick the saucony shoe you are interested in, and it'll ask you what mizuo shoe you are currently wearing (and also the US size you wear), and then it graphically shows where the Saucony would be tighter or looser.
Its US-only, so you can't buy from there - but there's no restriction on using the appl