I based the size for my boots on my running shoes(New Balance size 8 2EE). I also ordered a new pair of running shoes because my current pair are worn out. I got them today also, New Balance 715 8D. I tried them on and they seem to be half a size to short. So I am exchanging them for same style 8.5D.
I laced up my boots and walked around for a while and they seem to be to tight width wise. I think I am going to try to find a pair of 8W to give my toes some extra room. The boots that I got are 8NR(narrow regular).
The sizing that is used for combat boots:XN, N, NR, R, RW, W, XW
The sizing that is used for regular shoes: 2A, B, D, 2E, 4E, 6E
Based on my experience so far, I would say that the type of boots a person would select could be about 1/2 a size smaller than there running shoe. It also depends on brand of running shoe because not all brands size their shoes the same. A little wider to accommodate wool socks instead of cotton.
Please don't take this as if the "word of God", but rather something to base your decision on.
Semper Fi, Do or Die, Gung-ho Gung-ho Gung-ho