I swaped from easton EA50's to nukeproof flats,
I ride at Swinely and the difference is night and day, with a tiny 60mm stem, flipped to give a -ve rise and flat bars the 456 decends like its on rails, never once washed the front end out and the unweighted rear just follows through.
The tree thing isn't as bad as you imagine, sometimes its a case of tiing pedal strokes to rock the bike between a pair of trees but I've only come to a stop once and blamed the bars, and that was a momentum (too slow to flick the bike through) thing rather than actualy clattering both ends into the trees.
I found they make much more sense run really low, imagine your arms and the bar as a triangle, the wider the bars, the lower they need to be (or conversely the lower your bars the more benifit from wider ones).