I typically wear 46 for sneakers, running etc, but had to get the Supertechs in 45 for the length to be right. Unfortunately they were too narrow for my feet so can't wear them comfortably. In my experience they don't break in over time either, so make sure they feel comfortable right away.
I just went through this myself, I have a set of alpinestars Smx boots in a size 10.5 (45) and they are too big for my size 10.5 work boot feet. I had to wear 2 pairs of socks to get them to fit comfortably.
I just upgraded to the supertech R boots and order both the size 9.5 (44) and the size 9 (43). I tried on both sizes with normal work boot socks and I fit into both but the size 9 was too tight, and uncomfortable. So I stuck with the 9.5 and it fit perfect. Hands down the most comfortable boot i have ever tried on, feels like they aren't there when on the bike. A strange feeling at first compared to my other A star boots.
My suggestion is to order 1 size under the recommended sizing by Alpinestars and if you can afford, get 2 sizes under as well to try the difference and see what is more comfortable.