if it helps, here is a summary of my recent experiences;
i have just gone from 711mm havoc carbons to 780mm answer pro taper carbons. But i am 6ft3 and i just found the havoc a bit narrow.
bar/angle/control setup i have faffed with a lot and gave quiet different characteristics.
Mechanically there is a valid argument that a longer bar has a longer lever arm, we understand the reasons for this on stability but what it will also produce is greater vibration over a longer a length, the wider you go the more the vibrations. As pointed out above, carbon is inherently stiff, granted a 15mm difference shouldn't make a dramatic increase, however that assumes the construction is identical. To rule out the width argument try running the controls the same as the old bar position.
I did have narrow grips with my bike last year, which i quickly changed out to my old tried and tested favourite, and that made a big difference. Terrian i ride is 50% rocky as hell.
Certainly sounds an odd one