I have a pair of 320s and don't really like them. The upper is about perfect, but not enough forefoot protection from rocks for the trails in my region. And I'm not sure there's enough midsole structure for ultra distance. I do like the low-to-ground feel and light weight. Close, but not quite there for me.
Nike Zoom Trail is the best trail runner for my money. It has all the upside of Inov-8... light, flexible, low to ground, sticky outsole, ...plus a bit more room in the toebox, more midsole structure, and the perfect amount of rock protection without losing ground feel. Simple, effective upper. This is a shoe for forefoot/flatfoot trail running. I've done up to 100 milers in these shoes.
Some recent shoes I've used:
Brooks Cascadia (3 pair in 2007/2008) - too much midsole, uppers just did not fit me (pressure points), feels like I'm 'on top' of this shoe, rather than 'in' the shoe.
Montrail Vitesse (3 pair in 2006/2007) - low to the ground and locked the foot down nicely but I can't find them in my size anymore. outsole was terrible.
Montrail Cont Divide - un-runnable heavy brick, like low-top hiking boots. 3 inches off the ground. worst "running" shoe of any type I've owned.