I am a 6 wide and I ordered a 6M. I usually order a half size up if they don't come wide.Well, they are plenty wide enough, so I suppose they are true to size. A 6.5 would definitely have been too big for me. I hope this helps!
These shoes run big. Definitely go 5 or maybe even 4.
I ordered my regular size of 7 and they fit perfect. I tend to follow the details from STP as they will always indicate if shoe runs large or small. BTW, I really love them.