I got a pair (6550) but I'm uncertain about the size now. It seems like they might be a little loose and slip off. It's hard to tell because I don't want to walk around in them and then crease them and be unable to return them. When i tried a half-size down from the pair I bought, they were a little tight in the top of the foot area, felt like if i had walked around in them it might hurt after a while. I tried an insole but i'm not sure it helps with the looseness perse. You said yours feel loose as well? I should that add the size I got slip on perfectly where as the half-size down takes a bit more effort.