I preface this by saying that I'm no expert. I can't even tell you for sure how wide my own bars are (26 inches maybe?). But my suggestion would be to try the stock bars as is for a ride or two and see how they feel to you. Ride them on trails typical to the type of riding you do. Be mindful of accidentally clipping a tree if the stock bars are wider than you're used to.
For me, I wanted a bar with a bit of rise and backsweep, so width might be only part of the equation for you. Don't cut anything down until you're otherwise content with the bars and even then, cut conservatively and go for a ride before cutting any more (making sure to also read any manufacturer instructions for the bars). I'd add that I also have very narrow shoulders. On my road bike, I use some of the narrowest bars you can buy (Deda 4 Girls). In retrospect, I could probably have handled a slightly wider bar, but at the time, I was more afraid of clipping a tree than getting really good leverage.
Last edited by indysteel; 08-28-2012 at 11:54 AM.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher