When all else fails, I turn to SportBike Track Gear as they seem to be the only company that can provide, when no other can. I mean, it's ridiculously fast shipping and they seem to always have what I am looking for in stock. The local shops can never seem to keep their stock long enough due to having a low supply so I practically go in to do sizing than order from this company.
Now on to the product itself. I wear a size 10US in a Nike Free running shoe, 9.5US in a North Face winter boot, so I went with the 41EU in the AStars Super Tech R because the 42 was half an inch to big. The boot should be snug and comfortable when you are in the riding position and/ walking about. If your feet can slide in the boot while walking or your heal can lift inside the boot while in the riding position, then they are to big.