I tried them on at a store after measuring my feet 3 times during the day and coming up with a measurement. At first I thought they were way too small, even after trying them on in the store.
Your toes should press into the end of the toe box, I don't have any experience with the Injinji socks. Wear them walking only for 2-3 weeks before running. Wear them for walking as much as possible. This will stretch them out. Use the velcro on the side. Wash them after this period and they should be good to go. These require breaking in just as much as any other shoe (plus your calves need to be broken in for them as well, you'll feel them for sure once you start running in them).
I wear 11.5s and I got a 44, 45s and 46s were too long (my foot is probably an 11.25 using USA measuring). Ultimately it comes down to your particular feet.