As far as I know and experienced, O/S bars are not better. I've heard that they may be marketed for better control and more stiff and such, but I haven't really felt a difference in a good bar of either size. I would think the O/S bar would be heavier since it has a bigger radius around the clamp area. However, it seems to be much easier to find a decent O/S stem/bar pair than the old.. 26 or 25.4 or whatever it is.

Also, in my experience O/S bars limit the surface area you have to attach things if you have lighta and such since you can't really attach anything where the bar jumps from 25mm (or whatever) to 31.8 at the clamp area.

I personally would prefer threadless. How far off is the stem length? You could just gets bars that go deeper (and wider, for your other problem) which would give you a few extra mms if that is all you need.