Every time I've widened bars, it has improved the handling of the bike. I'm quite broad shouldered, so a 680 bar still felt a bit narrow. I'm now running 747mm bars, and these are perfect. If you've been riding long enough, you should have some feel for where your hands are, so I don't find them awkward in trees.
It also opens your stance out a bit, and makes you 'feel' attacking IMO. Apart from this, it lengthens the reach a little bit, but not noticeably.
I've found that since running the wider bars, I am pulling the bike up harder out of corners and generally just chucking it around a bit more. It's probably more of an attitude shift than a geometry change.
If you do end up with bars that are too wide, you can always break out the hacksaw.