I wear a size 46/47 street shoe and got a pair of size 45 vapours, they were tight but did stretch a bit, so a good compromise between comfort and fit was reached.
If its of any interest, I also have the force which are the same materials as the vapours albeit on a different last, and I bought these for all day comfort at a not too tight size of 46, but I can now wear them with socks as they stretched quite a bit.
In reply to marky: I wear a 43 steet shoe, and i'm on my third pair of size 41 vapour lace. (i'm told the velcro's are a slightly different last.)
There always very tight to start but break in perfectly!