Any twist you have will shoot them fine.  Generally speaking the best accuracy will be found with slower twists for light bullets, fast twist for heavies, in order to properly stabilize them.  Imbrog has the best range.  For sure, it's not worth buying a special upper just for 40's, unless you really want a dedicated "super-shooter", then a 1/10 or 1/12 would be a good choice.  Rifle barrels are funny though and nothing is guaranteed.  These are just places to start--bbls. are as individual as wimmins.  Imbrog will back me up on that, I'm sure.  [:)]