I'm a 6 1/2 shoe, have owned several Ryka's over the years- hiking boots, walking sneakers, skimmers, all in 6 1/2, all have fit me true-to-size and comfortable.
Occasionally I have seen reviews on items I've bought where people said their toes hit the edge so they sized up 1/2 size, but I've never had to do this.
I would start with your true size, unless you have an unusually longer big toe, or just like extra room, you should be fine.
Hope that helps~good luck!