I just got the 310's a couple weeks ago, I got them because I was nervous about going too light on a trail shoe. I also own Merrel trail gloves which I had taken out on day hikes. While I enjoy having better feel on my soles, I disliked feeling everything so well that my soles began to hurt after a few hours, haha.
I was thinking about the width issue just the other day, I find mine to be well-suited for my feet. I ran XC in high school, but haven't paid much attention to shoe companies since. From what I do remember on general fit was that NB was a much wider toe box than adidas and many other companies. To me, this one pair (sized a half up from my normal shoe size) of Inov-8s that I own remind me more of my old NB. Roomy in the toe box, but still tight enough on the heel.
I'm enjoying the feedback I'm getting from the 310's, but they have not yet hurt my feet (and I don't expect they will). I am far from having large feet though, and this coming weekend is the first chance I'll have to get more than 4-5 miles in one shot on them.
The pair weigh 670g.
Edited to add weight of pair and shoe model.