Often pondered on the handlebar width debate which seems to be in vogue at the minute.
Personally, I cut down 685mm bars to 665mm because they felt too wide for general XC and I’m 6’3″ with proportionally wide shoulders and arms in proportion also.
Cleverly, I bought a frame that was the right size, so I didn’t need to run wide bars to get my weight forward for more front wheel traction.
Anyways, in your position, I wouldn’t want to run 665mm on an all mountain rig purely because in today’s fashion it just wouldn’t seem right.
Things you need to really consider:
Advantage of wider bar is really more steering leverage and not getting knocked off line on fast tricky descents.
The disadvantage is threading between the trees.
I guess the faster and trickier the riding, the wider you should go with the bar.
Noting that World Cup DH Pro’s generally run 29″ bars and motocross bikes which are heavier, faster etc. generally are around 30″ in the handlebar.
No one needs a 30″+ bar for leverage, they need to get in the gym and build up some muscle.
In my opinion, anyone running more than 30″ on an all mountain rig has taken fashion one step too far. Chances are they also wear ‘carrot’ shaped trousers with elastic bands in the ankles. What’s that all about? I stopped wearing trousers with elastic bands when I was a toddler.