Always go one size up with running shoes. Your feet swell quite a bit. Rome is going to be warm, if you are fling out your feet may also still be slightly swollen from the flight.
There are several problems with running in off road shoes, I find that they just aren't responsive enough on the road but as you aren't going to be running at a fast pace (ie your 10k pace) this won't really be a problem.
I have used the Trabuco's and find them far more of a multi terrain shoe than a dedicated off road shoe, still I think they offer too much protection that may mean that your feet will get too hot but that's more personal.
At this stage I think your gambling whatever you do.
I have only heard good things about the Nimbus, it might be a safe option.